The issue was brought up again this week following the rejection of a music app backed by a well-known music artist. Part of the problem stems from the automated approach Apple often takes. That may soon change, however. Following yet another app rejection, it was tersely revealed that Apple's upcoming parental controls for iPhone OS 3.0 might give developers the chance to resubmit rejected applications and perhaps have their content rated as unsuitable for minors.
There's certainly a benefit to that approach. If Apple has rejected many programs based on content, as opposed to some other function, adopting and enforcing parental controls would be a mechanism to get those apps on the market. I'm sure a developer would rather be able to sell their program rated as “18 and up” as opposed to not selling it at all.
Even with mechanisms in place to allow apps with “questionable content” the chance to appear on the App Store, it wouldn't alleviate concerns of unfair competition where Apple restricts the sale of software they feel too closely mimics their own in-house features. It's their store, and they certainly can choose to offer only software they approve. It becomes an issue of concern, however, when they seek to shut down third-party software sites. It seems to me that their fan base would be happy with app store restrictions if there were third-party options – a compromise between controlling software and still allowing users to use their iPhones as they see fit.