The changes to the Play Store we mentioned last month seem to have taken effect. Now when you're checking out apps on an Android tablet, the home page and the tabs for "Top Paid," "Top Free" and the like will only highlight apps designed for use on tablets, at least by default. If you search for a non-optimized app manually, the full listing will use a "designed for phones" tag.
Check out these screenshots. Here's a DROID MAXX browsing the Play Store's home page, and a quick look at one of the featured apps, Cluster.
Ahem.Developers, if you want to avoid getting the "designed for phones" tag applied to your Play Store page, Google has some tips over at the Android developers blog. For everyone else, the changes should be appearing automatically in the Play Store on your tablet.