Oh, and Merry Christmas too. ;P
Personally, I'm of the mind that when you say "Happy Holidays" it's a universal greeting that wishes everyone a happy "whatever you celebrate", which includes Christmas, Hanukkah, Ramadan, Kwanza, Winter Solstice, and any other winter time celebrations that others observe that I either don't remember or don't know about.
Sure it's a bit of a cop out, but it's meant to simply wish everyone a joyous time this time of year. So, if you hear someone say that, feel free to say it back. I'm personally not offended if someone responds with the well wishing of a specific holiday, but I'm not sure what others are offended when they don't hear that specific holiday greeting. Christmas may be the most observed, but it means different things to different people and the different ways that celebrate it. That and it's not the only widely observed holiday out there. I wouldn't be surprised if either Hanukkah or Ramadan have it beat or give it a good run for it's money this time of year.
I dunno. It's just me I guess, but I like to be able to meet people on their own terms as well as my own and this I feel does that. ;P

Anyway, I hope everyone has or has had a wonderful season this year! Hugs and kisses to you all! Hope you all get wonderful pressies. ^_^
^.~