Microsoft has a reviewing process for the WP Store. They don't enforce a "this is another FB web wrapper so it's not allowed" kind of rule, but the rules in place for quality and stability are pretty strict.
It's weird that Microsoft apparently doesn't give a shit about trademarks or IP in their app store admissions reviews. That seems like it would make them liable if they actually manually give these apps a pass.
How does Microsoft know if a trademark is being used with or without its owner's permission? I mean, you can make a pretty solid guess in these cases, but it seems like waiting for a takedown request from the trademark owner is reasonable. (Full disclosure: I work for Microsoft, but in a different division, and I'm definitely not a lawyer)
How does anyone know they are hosting illegal software? Seems like Microsoft is doing something worse than a file host or torrent site. They are actually paying the criminal and themselves. Its perfectly sane to bring down entire website/ecosystem when it is found to host a movie or song. Is software IP less important than Justin Bieber new soundtrack? Were are the suits to knock on Microsoft's door when they turn a blind eye to what they are hosting and profiting on.
For the smaller trademarks, I'm not expecting every Microsoft reviewer to know about them. But for Facebook and Twitter? Yes, I'm expecting them to know something about that.