As with all applications, some update more than others. Though I have to admit, some of them "big" applications take forever to update. I've had applications update weekly, monthly, and some update almost never it would seem.
Originally Posted by dj9928
I guess one possible reason could be the whole resources issues within them companies (though no excuse for applications developed by Microsoft). The company adjusts resources according to demand and exposure. With WP7 having a low userbase it means that a lower amount of resources will be dedicated to the platform than to iOS, or Android for example.
All speculation of course.