I think given the precedent of you and DH hosting the party each year, it would have been better to let people know in advance. Not necessarily a full-family email blast, but maybe mention it to a couple of key people who could be relied upon to spread the word. That would have given other people time to step up and volunteer for the hosting duty, for example.
Also, it depends on how set your tradition is--if you always have the party on the Saturday after Christmas, for example, people may have kept that date free by default, turning down other invitations. On the other hand, if the exact date is more up in the air, and people are only now contacting you to ask about it (and only one person at that), one might infer in this particular situation that the lack of plans didn't really have a big effect on other people's schedules.
I don't think it was rude not to tell people--I would reserve that for a case where people had asked and the non-host had strung them along, for example--but in the future it might be better to let people know.