Whenever a new MacBook Pro comes out I look at what used versions of the previous generation is going for at various places. Quite often, the price is only a few hundred less than the new ones.
I think, "Well, it would be foolish to buy the older one when the newer is more future proof."
But, I don't think - "Man, if they can get that much for the used old one, then they're being very smart. Rather than spending $2.5k for a new one every 3-5 years, they spend $500 every year or so and always have the fastest machine and are always up-to-date on the OS."
It's a hassle, moving apps to different machines, etc., but there are hassles the other way too.
Presumably, if Apple keeps updating their iOS devices at increasingly rapidity, they'll want to move to a lease-like subscription model, too. "Join Super AppleCare for a $500 annual subscription and trade in your iOS device every year for the latest similar version, ..." Similarly with their laptops, etc. Lock-in the customers on the hardware side, just as the software houses have tried to do for ages.
The MacPros are a different kettle-of-fish, though, because they're so expensive and so in-frequently updated. :-(