Agreed. Mac applications do less, because the API doesn't allow them to do more without jumping through hoops. There is also almost no third party Cocoa frameworks for Cocoa, which doesn't help either.
I don't know about that. Some Mac apps do a hell of a lot considering how bad some of the API's are. Delicious Library is a great example of that. The barcode scanning feature, uses any iSight or digital camera plugged in to scan barcodes off of books/DVDs/CDs/Games, is an example of this. I think a lot of the Mac apps do less because they realize that piling features into an app just for the sake of features or trying to get the 1%-2% of people who might use those features isn't worth the time or effort.
Mac developers are enamoured with Cocoa and ObjectiveC, but they would be enamoured with anything Apple gave them, because they actually haven't got a choice. If you dip into Mac developer forums though, you will see that they do spend just as much time fighting with API bugs as anyone else. If Apple did release Cocoa for Windows, they would get a lot of Mac developers releasing apps for Windows, but I don't see Windows developers rewriting all their stuff in Cocoa, just to run on Macs.
Mac devs are enamored with Cocoa and ObjectiveC because they toiled and slogged through the Mac toolkit and Carbon API for many years. It's the same reason that Windows devs liked the .NET Winforms namespace when it was first released, warts and all, after having suffered through the raw Win32 API and GDI for so many years. If you've spent all your time with 100lb weight on your chest, moving down to an 80lb weight seems like heaven.
IMO the strength of the Apple platform doesn't lie in the Cocoa framework. It's in the Darwin kernel and the Quartz graphic framework.
That being said, the Leopard release will bring some HUGE changes to the Cocoa framework. Garbage collection being the one I'm most looking forward to.