I suspect that in most cases where people need a very high end machine for work, price is not as much of a factor as running the software (including OS) that you want.
Having very demanding needs in hardware specs but flexible on operating system is probably a relatively rare occurrence.
Apple's the one that has strong ideas about how you should spend your money. PC makers listen and deliver a diversity of products.
Now, I'll grant that Apple products have advantages in terms of stability because there is less finger pointing when things go wrong -- you could get a mac laptop that sleeps correctly about 3-4 years before windows laptops got it right.
I don't see any real U.I. advantage on the Mac; if you try to put your photos in a movie, for instance, the Mac will drive you absolutely up the wall because it wants to make you look like a Shmuck who can't turn off the Ken Burns effect.
I'm going to guess the Lenovo W520/W530 or a Dell Precision Mobile Workstation. Those are the major laptops I know of that come with 4 DIMM slots (32GB now, 16GB last year because 8GB DIMMs were crazy-expensive).
Currently sat at my w520 and it's a brilliant piece of kit. I've always been a thinkpad fan - although I can appreciate the draw of the MBP.
It's little touches like the spill-proof keyboard, carbon fibre reinforced plastics, trackpoint, and amazing thermal management (even with an i7 in there the bottom never gets hot, only mildly warm).
I had to buy a laptop recently and chose a PC because I could get 32G of RAM in a PC laptop. For my work, I need that much.