..to expect people to reply when I put RSVP on an invitation

[WeWhizzzYouAMerryXmas]

...rather than just going "Oh, thankyou" followed by a vague comment about possibly thinking about coming if X Y Z happens. Grrrrrrrrrr

I know it's near Christmas BUT I don't mind if people say they can't come - I just find the vague possibly maybes rather annoying

If they don't get back to you by the date then just assume that they ain't coming. That's what the RSVP is for.

It is rude of them not to tell you, although people do have an awful lot going on at this time of year I suppose.
Aswell as xmas, Iv also got my ds's 3rd birthday party on the 23rd!
But, no, yanbu.