As a long time tower-style Apple user (G3, G4, G5, Mac Pro...), I love this perspective from Hypercritical's John Siracusa:

Why is this important? If Apple produces a new Mac that’s faster than any of its current models by leaps and bounds, will people suddenly buy it in huge numbers, choosing it over the laptops, tablets, and phones they prefer today? No. Is it because a very fast Mac can be sold for such a high price that its huge margins will make its profits significant, despite the expected low number of sales? No, that won’t happen either. Is a new, insanely fast Mac even guaranteed to make any money at all for Apple? Sadly, no.
So why bother creating a true Mac Pro successor at all? Good riddance, right?

I like where he goes with this article.