It might also have to do with the concern that on mobile, the like button could be somewhat disguised visually and might it might not be immediately obvious that liking on the app will mean liking on Facebook.

The big problem on mobile is that the Like button is extremely tiny, and not all platforms can utilize the iFrame version of the Like plugin. By making it available through an Open Graph action, developers can embed it into apps, on web pages with a better target than the standard Like button, and on web pages as well in a way that fits the design scheme of the website.

It seems like it allows Liking of any page with Open Graph tagging, only question I have is if you can use it to Like a Facebook page still. I plan to test that out shortly, probably tomorrow.