When all the iPad apps launched on Friday I was surprised to see this. If you look at the screenshots you can tell it is not an official app but boy are they making bank from all the people who don't read reviews and don't pay too close of attention.
I hope Facebook sues them for unauthorized use of the Facebook name/logo.
Maybe it's because Joe Hewitt 'quit' developing for iPhone because he was pissed at Apple.
They released 3.1 almost immediately after that, but there hasn't been any significant updates since Hewitt left.
A source of mine says that the next version of the iPhone OS may ship with very tight social network integration and social features built in. Perhaps Facebook is putting off writing an iPad app because they're working directly with Apple on integrating with the 4.0 OS? It wouldn't be that unlike Apple to do something like this -- look at the Google Maps app as an example. Just a hunch.