Er, I can buy last seasons model all the way back to VERY old Macs in a number of places. Apple only sells NEW machines through licensed dealers. There is a vibrant market for used and refurbished (I just bought one - from Apple) Macs. So much so that it keeps the price up. (In the states we call that supply and demand). Fact is, even as far back as the G4 processor series will run the latest Mac OS. That means Apple is consciously supporting three processor families that go back 10 years. Apple literally trash canned the G4 and G5 in favor of a completely new (to them) processor architecture, yet I can still run OS X on my G4, G5 and Intel Duo Core.
By “refurbished” you simply mean “used,” not factory refurbished.