The only thing that I'm worried about is that they might be expecting a gift back and I have no way of telling it. If the people on eHell were on the other side-that is, if you were giving the gift-would you be hurt if someone didn't reciprocate, even if exchanging gifts had never been mentioned?
I have (very recently) been on the giving side of this--I gave friends birthday gifts, but received nothing in return from either of them when my birthday came along.
Did it hurt? Well sure, a little. Gift exchanges are fun for me and I look forward to them. But it also sent a clear, polite, confrontation-free message. I didn't have to ask if they wanted to exchange gifts for Christmas, I just assumed they were no longer interested (and I was right.)
It did NOT change our friendship, it did not make things awkward--I figure these are the things you might be concerned about.
P.S. Something to think about is, do you believe these people would happy receiving a gift from you if they knew how little you wanted to give it? My vote is no. (Obviously there are gimme pigs out there, but you said these people are your friends!) Disappointed as I was with my friends' decision, I would feel much worse if I thought they were being unpleasantly burdened in gifting me.