In days gone by the motor industry talked about cars of the future being sealed for life - a vehicle that you drove out of the showroom and then didn't have to return to the workshop until the car had reached the end of its useful life.
It never happened, of course. The motor industry realised the most profitable part of being in the motor industry was the servicing and maintenance regime. Keep them coming back and spending. By stretching warranties and bumping up labour rates, as well as the hefty markup on service items, the motor industry, as a whole, has managed to survive and in some cases flourish, in challenging times.
The PC industry is seeing a similar challenge. In days gone by enterprise replacement schedules meant that PC manufacturers were benefiting from reselling new equipment every three years. The consumer market followed suit.
Two things happened to change that. Firstly Windows XP arrived and cleaned up the operating system's act. No longer would the very act of using your PC cause it to get slower and slower.
At the same time the demand for processing power from applications levelled off. Sure, games and certain niche applications still demand all the power you can provide, but for most users email, web browsing and Office applications are about as strenuous as it gets.
So now the PC industry has some rethinking to do. Some manufacturers have embraced the abandoned future of the motor industry, with sealed for life designs, motivated by a desire to fix the life of the machine to that of the first major component failure. Others have been more flexible about the ability to upgrade machines - adding memory and replacing storage or batteries are trivial for these machines.
When the time comes to upgrade your machine the long term viability should really factor into your thinking. There's no reason why a new machine shouldn't provide a minimum of five years service as far as performance goes. You should be considering how component failures and the complexity of repair will impact that capability when making your buying decision.