@orbital~debris
It could very well be the waxing and waning of platforms over time. And It seems like the Mac could be heading down the path of the iPod at a slower pace.
iOS devices make u upwards of ~66% of Apple's revenue/profit (i can recall the exact numbers), and it has been growing over the past decade, which means that the portion earned by Macs has been relatively shrinking.
I remember back in the day when the iPod came out, Apple was trying to capitalize on the 'halo effect' and so kept their Macs up-to-date and competitive. (maybe cause the Mac was a much larger portion of their bottom line back then?). That doesnt seem to be part of their plan these days. (A missed business opportunity if you ask me)
The above is all just one big excuse for them to let the Mac line languish.
Quite frankly, at the very least, instead of major hardware design refreshes (MacPro), they could have instead retained form factors (unibody MBPs tower Mac Pro, etc) and just kept the CPU, GPU, RAM, SSD, prices up to date. Small iterative steps regularly. IMHO
I really wonder how much their negligence of Mac hardware is effecting their sales.