Sam mentions on the forums, and subsequently on the blogs, that bows didn’t make it into the game, after the guys tested it and found that actual guns blow it out of the water. Crossbows are still cool, though. Via PE.

Bows just don’t work in Fable 2 and so, there won’t be any in the final game (OK, never say never, but at the moment there won’t be any bows, and if it changes, I’ll let you know). [...] Probably the most important reason why not, is that it’s just silly.