You might have misread something because you are still allowed to post the pics that were drawn for you on Weasyl.
According to Paragrah I.A.2 on Weasyl Community Guidelines:
"Original Content Collections: If a particular work has been uploaded to the site and was created for you, includes you, or features one of your characters, then the original uploader should offer it to you as a collection. If the original creator does not have an account on Weasyl, you may post the work to your submissions gallery."

Emphasize the should in the first part of that paragraph, as a reccomendation, but not as a requirement.
And I do see anywhere else in the guideline where it is against the rules to post the images even if the original artist has an account on Weasyl.

The "should" is significant. Even if you paid for a work, you're not guaranteed a right to display it. And, off course, the artist might choose to delete the work or withdraw permission.

If the artist doesn't have a Weasyl account, then the art can be posted - but the Weasyl guidelines urge the commissioner to try to persuade the artist to join Weasyl.

In that case, what happens to the user's right to post that picture? Now it's outside the rules, unless the artist uploads and approves it. Popular artists who join Weasyl would have to upload hundreds of old images and assign collection rights for each one individually. I don't see many doing that.

Overall, I think it's a lot more trouble than it's worth.

I asked this question to the system ops of Weasyl back during beta. The community guidelines are worded poorly, here is their official response when I asked about items I had commissioned from artists that were already on the site, but did not have the pieces I commissioned up:

"We ask that you attempt to use our collections system, however if this is not possible for some reason you may upload it to your regular gallery."

The collections system is there for the sole reason of reducing duplicates on their site to save bandwidth. If the image is not in an artists gallery, you have every right to upload it yourself, provided the artists gave you rights to the image when you commissioned them. The whole reason it's worded like that is to try to encourage people to make sure they have the artists permission, and to make sure it's not something already on their site.

If you have any questions about their policies, they're very friendly people! Just pop an e-mail over to weasyl.sysop[AT]gmail.com

Wow. That's pretty awful policy. This kind of contractual stuff really should be kept between artist and commissioner. I think US copyright law actually gives the commissioner complete control over works performed for hire, so this is really asininely backward.

I get the feeling that this is a case of a software engineer's pride getting in the way of legal reality. I can imagine how it might've happened: someone was really proud of their fancy gallery-sharing feature, thought it would end all redundant "new submission" messages and save them disk space, and is trying to force everyone to play along.

I can understand wanting to avoid redundant data in their system, but that should be done behind the scenes (i.e. image similarity search), not by putting stupid demands on users that curtail commissioners' rights.

See above (or below). The policy wording is a work in progress, but the purpose is to save server load by referencing one file and reducing duplicate uploads. They're putting a lot of effort into making the site more cleanly functional and reliable than FA. This is one of the ways they're dealing with the problem of heavy use while keeping costs down.

The goal is to encourage people to use that feature where they can, not to restrict people in what they can submit themselves.

I agree that this is better done on the back end. Hopefully they have something in the pipeline to hash check submissions and suggest matched collections. This is however a somewhat complicated task to accomplish effectively because you either have to upload the whole file and have the server check it, or download an applet that checks it on your end in the browser before sending it to the server. Both require bandwidth overhead. One requires more server processing load, and the other requires a lot of complicated coding and scripting integration that could contribute to site bloat. An heuristic image comparison would require a LOT of server processing load, and so wouldn't be practical, not to mention may throw false matches when variant images or different resolutions are involved.

Even if people do use it voluntarily, the permissions model needs to be appropriate—the representations of the image in the commissoner's and artist's galleries (or commissioners' and artists' galleries if there's a large collaborative work) should act like equal symlinks to a neutral file. Once you allow someone else to include it in their gallery, then they should be able to keep it there even if you decide otherwise.

As long as one party can exert asymmetric control over the file there's a problem. Even if that's unavoidable, the policy decision to make that party the artist is directly in conflict with US copyright law, since commissions constitute works for hire and are the property of the commissioner(s).

Unless I'm mistaken, that's already how it works, or at least how it's intended to be implemented.

...well, the poster of this journal doesn't seem to think that's quite right. *shrug*

You can, actually.

Call me old-fashioned, but I think FA got all it needs as it is. Also, ownership rights are important, but while the great majority of artists who charge money for art here are really honest and trustworthy, as well as their comissioners. A little faith and trust does the trick around here. Doesn't it? ^^

What Mabarial said. The policy is worded poorly and should be updated, but in the meantime they want to encourage people to use the collections feature because it saves them an additional upload as well as the duplicate file on their servers (and thus storage space, and money). If for whatever reason you're unable to use it for a submission, they're not going to have a problem with you uploading it yourself.

I personally am waiting for them to flesh out their written submission features before I really make use of the site, but I think it has a lot of promise.

I still think it's bad to try to implement this via rules.

A little bit of clever software could achieve the same effect, without ever bothering users. This method is just dumb and intrusive.

I agree. The rules are a work in progress and will probably be updated. There may also be something like a hash check on upload in the pipeline, which would be a better solution. The site isn't done yet so I wouldn't be surprised if some of these features get fleshed out in the relatively near future. I'm still waiting on written submission support beyond plaintext, myself.

You can always contact them directly or suggest it as a feature, and see where they go with it. They seemed pretty receptive to suggestions on their forums from what I've seen.

Anyway just my 2c.

Yeah, a hash check would do the trick. But it isn't my job to give them advice.

I have no stake in this, other than not wanting to have to subscribe to many different sites just so I can follow my favourite artists. Maintaining this gallery and keeping track of who I've commissioned to do what, is already enough work. XD

See, you could have just said that :p