You can buy an upgradable computer specced to your current needs today and adapt it to your future needs as needed. You will pay less now because it doesn't need to be able to run now the OS that'll be available in 5 years and you probably will pay less for the capacity by then. The cost is the time you'll need to invest to make those upgrades: sourcing the parts, assembly, etc.
Upgradability is, in general, a good thing. In the case of these laptops, you buy them to the specs you'll need at the end of the machine's useful life, at the full current price.
