Think about the staff, for a second though. You know how annoying it'd have to be, changing anyone that's ever won a monthly contests title whenever they wanted, just because?
I think having it set for a month adds an incentive to keep up what you were doing in the first place. This prevents schmucks from being good, winning a title, then being a lil shit.
The point of an incentive is to make people want to come back, not to give them something and have that be that.
It should only be for official, site sanctioned contests.
Anything member-made/member-hosted would just be a slippery slope that leads to bias in voting and overall douchiness to avoid having someone win.
So nay on that.