That could easily be fixed by bringing the price back down into reality (i.e. 30-50% more expensive than equivalent x86-hardware, but not 300% more expensive).
Currently you'd have to be lobotomized to buy a MacPro at this price point. You can buy literally 2-3 "beige boxes" with similar specs for that money.
The shiny case and OSX make up for a lot, but there's a limit to what people will bear.
The entirety of worldwide PC shipments for a quarter is less than 100 million units. So, no, cutting prices is not going to help catch up to iOS revenues.
Exactly. Apple may be figuring that if they could divert the resources currently devoted to the Mac Pro line to other products, they would be making a greater return.
Or perhaps they have something in the pipe but not ready yet. They've never been a company to tip their hand early.