IMO if someone has a 10 year old pc and can't afford to upgrade it then the likelyhood of them buying you game is 0.
Nicely put. In which case the guy buying a new computer has the likelyhood of '0' to buy your game.
Except if he's just bought a new computer, just to play your game, he's not going to not want to buy it next month. Win/Win situation if you ask me. He gets newer hardware, you get to write more games.You have to look at this realisticly. What's more expensive, new(ish) hardware, or programer hours? If you can buy a Dell PC for arround £250, there's little reason to spend £5000 on programmers to optimize your code. It's just as cheap to buy those 20 customers with old computers a new one.