They posted the app’s source code, violating the iPhone-development NDA. If the NDA’s actually being enforced, that’s certainly enough of an offense to get an app pulled.
It’s interesting that they changed their name from “Box Office” to “Now Playing”, though — maybe there was a trademark problem?
The open-source WordPress app is still up. I’m guessing that whatever caused Metasyntactic to change the name of the app was also what caused Apple to de-list it, and it probably wasn’t anything sinister by Apple.