I agree! It's not easy to measure this and my equation of course falls a bit flat. But as a rule of thumb I think it'll do. Albeit more so for the games I tend to play I guess.
My question stems from having seen people complain that pricy games were to short. I'm kind of thinking about it like a cinema visit you know? If you enjoyed the movie that was 2h and cost $10 (taken willy nilly from the air), how could you equate that to a game?
That's pretty much my look on things as well! I've felt like the gaming community generally demands more out of a game than they'd a movie.