> Better yet, why didn't Apple just let the iPad replace the Air if "all they need" is web browsing and office clients?

Well, they are. Remember apple's "what's a computer?" ads last year? And the higher end ipads cost more than the lowest priced macs.

They make different products for different use cases. Personally I do development on an macbook air, which is already so light I sometimes have to check my bag to make sure I haven't forgotten it.