The App Ecosystem
This is why I feel the issues regarding lesser number of apps is blown out of proportion. More than half the apps which people actually download are not used at all beyond the first few times. Its important that MSFT focuses on getting those which are having high MAUs and making sure that future good apps are released simultaneously on WP too (like Angry Birds Star Wars). There's no point in getting 900,000 apps on other app stores that arent even used by people daily. Getting something like Draw Something just because it has high registered downloads on other app stores will be of no use.
Another strategy they should probably follow is to focus on developing good first party apps, like they did for the Xbox using Bungie. These first party apps could showcase the best features of WP and Live Tiles (which are horribly under-used by app developers) This is what they had done with the Xbox when most 3rd party titles were being developed for Sony.