There are many people using Windows that might be interested in switching to Linux, but they would like to know how many of their Steam games run on Linux. This feature would really help out with that, especially for users who have hundreds of games in their library.
+1 Never understood why this isn't an option. Related to it is showing Windows content in Linux for things that work in Wine or are otherwise ported. Quake 3 Arena for example works fine with ioquake.
There are many people using Windows that might be interested in switching to Linux, but they would like to know how many of their Steam games run on Linux. This feature would really help out with that, especially for users who have hundreds of games in their library.