Noncommital reply to a party invitation.

I do not host that many party but if I do, I want to know how many guests I will have so I can prepare the sufficient amount of food.  One of the reply I get from those I invited that piss me off is the noncommital one.  "I am not sure if I can make it."  "Maybe."  "I will try to make it."  Yes perhaps it is true that some of them are not sure if they would finish their prior engagement to make it to the party.  But I think some of them are just not sure if they would have something else better to do than attend the party so they won't commit to it in case something else comes up.  Maybe some of them are not that thrilled to begin with to attend the party so a noncommital reply is their fail safe reply.  I would much rather they say they can't attend or commit that they would come.  So if I get one of these noncommital reply, I just simply text or write them "Sorry you can't make it to my party, so have a great Christmas/New Year then.  See you some other time."  This way, I made it clear to them that I am no longer expecting their presence.  Sort of my way to "un-invite" them.