Another reason for developers to consider tablet designs for their apps
Just as was previously announced, the Play Store is undergoing a few changes for those with tablets today. Although it has been an option for some time, when browsing app categories on a tablet you'll now be shown apps that are marked as "designed for tablets" by default. In addition, any apps that haven't been updated to be fully tablet-compatible will be marked as "designed for phones" under their title in the Play Store, giving you a warning of sorts that the app may not work properly.
Google is taking this opportunity to remind developers how to make their apps compatible with tablets, as well as to go above and beyond to make experiences that are preferable on tablets rather than simply compatible. Through the Developer Console you can simple head to the "tablet optimization tips" area and see what is keeping your app from being listed as tablet ready.
Source: +Android Developers