There was a time I would say that a strong Mac line was important to the growth of iDevices, but anymore with OTA updates and cloud services the iDevices are becoming pretty much standalone devices.
If you compare the wild growth of the iDevices to the comparatively slow growth of the Mac line you must acknowledge that the majority of iDevices are being purchased by people who do not own a Mac. I have never seen a breakdown, but the Mac marketshare is much too small to be driving record iDevice sales.
The Mac is still important to Apple, but I really think we are at a point where Apple sees the Mac as a PC era device and the iDevice as the future. What that means is the Mac will see less and less investment and updates whereas most of their focus will continue to shift to iDevices as we have seen over the past few years. Windows PC builders will still offer workhorse PCs, but it is not a real profitable market. Apple will continue it's shift towards catering to the most profitable areas.
Look at the Mac Pro and tell me that Apple still cares a lot about the professional desktop market? They don't. The iMac will probably see one more update if it's lucky and then I predict it will die a very slow death over the course of 2 or 3 years. Moving ahead Apple will continue it's focus on the wildly growing iDevice market and to a lesser extent on it's portable Mac line. Basically Apple is going to let Windows have what's left of the desktop market because even though there are still desktop lovers like myself the profit margin and growth just isn't there anymore. Sad story, but true.
Now bring on the iPad Mini. People are going to go NUTS over it! Mega bucks for Apple!
Look, I get what you're saying. And at some point in time your analysis will be ripe. But the battle for the post pc (aka mobile device) market is still in full conflagration, and Apple is not about to walk away from one of their advantages in the battle. Especially not when they're making a handsome profit on every one they sell.
And your statement about the Mac Pro kind of makes my point. The Mac Pro doesn't sell iPhones or iPads. The iMac still does.
Apple decided several years ago to stop battling MS, Dell and HP head on in the enterprise segment. They did this for two reasons, IMO. First, they would be battling from way behind in an ever shrinking market. So even if they made headway, they wouldn't get great return for their efforts. Second, the iOS devices and, to a lesser extent notebooks are winning turf in the enterprise coming in through the back door.