Well, it used to be like that anyway, I played many games for more than 100 hours, like Oblivion, Morrowind, Diablo 1 and 2, Civilization series, even things like Mario Kart, console RPGs of the good old days... Some first-person shooters like Team Fortress 1-2, Counter-Strike, Call of Duty 4...
All of those are excellent games, well worth the money. F3 like you say falls short, and doesn't have the replay value.
There's someone I know who says that a game shouldn't be longer than 10 hours, even if the game costs £40. He says if a game is longer than that, you won't have the time to complete it and play other games.
Maybe he's just trying to prop up the economy? If he spends all his time on one game the industry will collapse!