Don't forget that some of the so-called "older apps" were in development even before the contest started. Such was the case with StackMobile, StackApplet, so++, and SOwhat.
And alot of the older apps have had plenty of time for improvements and modifications, so they probably deserve the votes they have.
Having said that, I only released StackCenter 7 or 8 days ago - and it has 5 votes already. I released StackMail nearly a month ago and it has 2 votes. So clearly the content of the apps counts more than release date.