We have a lot of Macbook Pros and some Macbook Airs in our office (designers, mostly, plus a bunch of writers and a photographer.) They do seem to last awhile, certainly longer than the inexpensive PCs that other departments use, though of course many of those folks travel with theirs.
So cheaper PC kit that gets taken around the place doesn't last as long as more expensive Apple stuff that sits in an office. No surprise there.
My last PC laptop lasted as long as my MBP, but then they also cost about the same to buy. £2k
Which makes me think, Richard, why don't you simply buy a nice PC for the similar price as you would spend on a Mac? Possibly much power for your money, it was last few times I looked.
Unless there is a pressing reason to change, say to use Mac only software, there's no particular benefit. Both systems are very good and very annoying too.
But once you are in LR/PS etc it's hardly relevant what system you are using.
Also I'd say that if I didn't live near an Apple store, I probably wouldn't buy Apple products. But having one 15 mins away is really handy as all my Apple kit bar the barely used Nano have been back for multiple repairs or exchange.