I have to wonder if Foxconn or whomever was making these in Asia decided that the volumes were getting too low to make these at the prices Apple was used to.
It's not enough money to worry about. Foxconn would assemble them for free if that meant keeping the iPhone/iPad business.
The Mac Pro is very easy to assemble, but is large and heavy to ship from China to the US. It would make sense to assemble closer to the target market.
There was very little engineering in the Mac Pro that hadn't already been fully amortized. They're not like the rest of the product line, where there continues to be serious money and effort spent to refine manufacturing processes.
