This is something I've noticed with WP7, On iOS and Android apps are updated every month, on WP7 apps could go months, or in the likes of Twitter years before updates. Why is this?
Or it could mean that with the ease of creating apps for WP, not many bugs and not much left to do. With nearly 200 apps/games I get updates petty much daily for something. Some apps update frequently while others have never been updated. Has to do with the interest of the developer and/or the potential for income as was lreasy pointed out.