The basic need for support and bug tracking is a hard problem to solve, because users are stupid. If apple puts a bug tracker on the app store, any moderately popular app is going to end up with a huge mess of 'durrr... it doens't work' and 'hey developer your a fukhead' type comments. Even in the open source world, where the user base is generally more competent and savvy, the bug tracker is never front and centre on any of their websites - you've got to go looking for it and create an account, and most of the big projects still have a problem with useless bug reports.

Bug reports from the general public are simply not of any value. And building a support forum into the app store creates an expectation of support, which for most $1 apps is an unrealistic expectation. The developer has a facility to communicate with the users: the release notes on updates. The users shouldn't get a facility to communicate with the developer, unless the developer wishes to provide that facility outside the app store.