It definitely should not. Gamers use it because there are a range of genres of game. JRPG's ala Monster Hunter and Disgaea are pretty much a 300 hour minimum. There is no way GTA ever produces something worth 300 hours of gameplay, the closest they've gotten is their Online versions which frankly, would be horrible if they were priced per hour.
Racing games would have very little merit in price per hour. Sports games probably in between.
Then there's the whole fact that pacing can be implemented at the whims of the creators. It takes 4 hours to get energy so you can continue? Well, that 4 hours of paid playtime baybee, payyup!
How about games with little to no story? Should the new CoD only be $25 because it's campaign sucks? It's short after all. Or will they try and include multiplayer time, you know, something independent and timeless. Will they become arcades and start charging you per round?
Horrible, horrible idea. No matter hour you look at it, hours per game are only good for gamers with specific intentions, be it their limited time, their desire to 100%, or to see if it simply respects their time in the first place.
WadeTheWizard