Slowing Mac Sales?
Well considering there hasn't been a lower end* or a higher end computer (Mac Mini/Mac Pro respectively) for about 3 years and still try to sell them at "modern" prices could be a reason why.
Also consider how hard it is to upgrade the any of the current line when the time may come.
*I'm looking forward to a new Mac Mini myself. Be fscked if I'm spending that much on a 3+ year old computer now though.