If it makes sense for Google to invest in Android "so that people will spend more time searching for stuff online" it sure as hell makes sense for Facebook to create a chat client so that people will spend more time using Facebook to chat.
1. Google currently get fairly guaranteed income from its search. Facebook hasn't reached that level yet.
2. Having some people online more chatting might make some other people actually want to be online less. I'm happy that no one ever pops a Facebook on me. For a number of friends, Facebook as close as I want or need to be much of the time.
