When a game comes out, it needs to run fast on the
current "average" machine of the target group.
The argumnt, that people can upgrade is wrong, since
this would mean, that the game runs smooth wehnever the "averag" machine has evolved to the required level.
By this time the game is outdated/past the sales period already.
I even think that a game developer should not run and test
the game on his mostly higher than average machine.
This is one of the reason seen here often in the forum,
why games run choppy.