This is an interesting thread.
My mom won't use FB, but will sometimes complain when I mention something funny or neat that a family member posted because she was "left out". I will occasionally send her stuff that I've posted, but only when I remember to, which isn't often.
A friend of mine "left" FB for G+ (FB account is still active) and she almost missed a party I had because I had used FB to do the invites since everyone I was inviting uses FB. I'm glad she made it to the party, but honestly, it's frustrating to have to remember that she no longer uses FB.
I see both sides to this, I guess. No one should partake in a practice they don't want to just because it's the "norm", but I don't think we can reasonably expect friends to remember that you're not in the norm.
If they're like me, I truly forget most of the time - so any slights are completely unintentional.