do High Scores matter.

I think what really makes a game replayable, and thusly to the need for high scores and competitive elements like that, is not so much the length of the game so much as the depth of the game mechanics. Games like Super Metroid and say, Quake, get replayed just as much as any arcade style game, because of how deep the game mechanics go. If there's a system that's well designed and keeps players interested, than the length of the game won't be a factor in determining how competitively it'll be played.