Often when a game is on Steam, the developers forgo the use of other forms of DRM and just use Steam as their DRM provider.  They are not always completely DRM free outside of Steam, though.  For example, Telltale's adventure games on Steam mostly just use Steam as their DRM.  The retail versions of those games use SecuROM as their DRM.  Because it wouldn't make much sense and wouldn't be of any value to say that all Steam games are using Steam as their DRM, it's only beneficial to indicate when they use some other form of DRM and just indicate that it was the Steam version in the comments.  That is the reason for including the store that you bought it from in the extra comments.

I just wanted to put this information out there so someone didn't accidentally buy a game from their local store thinking it was guaranteed to be DRM free when it might not be.

P.S. This is true for all stores and not just Steam.