So apple should go out of their way to add support of other manufacturers devices to a piece of software they do not charge for rather than the work be done by the company making a profit from the sale of said hardware?
Especially when the iTunes library information is available for anyone to use as well as the sync services framework? At best, you get pretty much the same information that you could get from iTunes all things considered.
Besides the branding of iTunes, what does integration get a third party player?
Movies? No, they can't use purchased movie content because of the studios legal usage of DRM that they have an outside agreement for. iTunes couldn't provide that even if they wanted to.
TV Shows? No, same reason.
Podcasts? Those aren't unique. All the podcast that Apple offers are probably avaiblabe to anyone using RSS, Apple has a large directory sure, but theirs is not the be all end all.
Music? Yea, but you can get that from the Library information track plus the tracks themselves are in documented locations.
Applications? No. There's nothing for other handset makers can use - they all use their own incompatible SDK's.
All iTunes is is a front end interface to decode DRM thats already limited to Apple players with no change there. Any player that does get into iTunes would face huge barriers and limitations. How would Palm feel if their users complained about their inability to play TV shows or movies with their Pre? The only thing Apple could offer is the usage of unprotected music. They already offer that with the XML file.
Every player would face limits with iTunes that would cause the end user more problms than its worth. Using third party software is or first party actually a better solution instead of a patchwork solution system that ultimately will rely on vendors agreeing on things. It may sound nice, but it just isn't practical.