Rereading does bring something of the Apple Mac ecosystem to mind that isn’t mentioned directly (and rarely mentioned in the forum I think), the relationship of the sales of one Mac to another for a user.
My guess is that many (most?) Mac Pro users also own another Mac. Likely that’s a MacBook Pro for portable use. I imagine some own MacMinis as desktop for lighter use in the home. I wonder how many MacPro users also have iMacs. In my own case I have a few generations of Mac Pros, MacBook Pros’ MacMinis but no iMacs. I don’t know what the norm is though.
One thing a multi mac user runs into is peripheral compatibility across Macs. One might have accumulated several TB2 peripherals to use interchangeably between Macs. If one busy a new MBP with TB3 you can certainly adapt your TB2 peripherals. If you buy peripherals to take advantage of TB3 it’s pretty much an island though.
I’m wonder if they considered how the stagnation of the MacPro had a ripple effect on whether to upgrade other Macs. I certainly think it would impact peripheral makers if people are reluctant to buy the latest (TB3) peripherals since they lack the interchangeability until the user can replace Macs with newer models using the same technology.
Even though the Mac Pro makes up single digits it may impact the uptake of TB3 which is why a more “professional” iMac is that much more important. But for those who’d prefer a Mac Pro there’s less incentive to move to TB3 (upgrade other computers) until a TB3 Mac Pro comes to market.