Your assumption that apple is one big group just going from one project to the other is unfortunately misplaced. It would be a reasonable statement to say no iphone OS X development was delayed during any of this Itunes releases as they are more than likely two different teams with their own separate Iterative and incremental development cycles. Have no fear, your update is coming.
If that were the case Leopard wouldn't have been delayed from what Jobs admitted was a lack of man power due to concentration within Cupertino on the iPhone. As well, there hasn't been a big update for the iPhone since its release, just minor ones, and updates to keep money and control to the RIAA (while pissing off a lot of iPhone owners). Also, Apple has an admitted history of not wanting to hire more and more people within the company, as Jobs wants to keep Apple, Inc. small, micromanaged and controlled. Thus, it would stand to reason that the manpower utilized in producing minor updates to iTunes in order to keep people from making ringtones out of music they already legally own is taking away from other departments such as focusing on major firmware and software updates (cough*leopard*cough*cough*). In conclusion, no, there most likely aren't two different teams. I highly doubt there is an "iTunes Ringtone Licensing Watchdog Team" and a separate "iTunes Programming Department". In fact, I have an acquaintance Ben who is a 20 something programmer for Apple, hired fresh out of Buffalo from college, who pretty much has supported this fact.