Well, if someone can't even be bothered to finish the game, they're less likely to be willing to invest in future titles.
But then, if the title isn't compelling enough to finish in the first place, does it really matter if it's 2 or 10 or 40 hrs long?
Ultimately, I guess it depends on what the actual content of the game actually comprises of. They could add random dungeons with useless combat in it to appease losers. Or they could cripple the player's walking speed. Win-win!