I know what you mean. Monday Night Combat, a downloadable third-person shooter, is 800 Microsoft Points, or $10. Therefore, I am appalled that Microsoft and Sony have the gall to charge $60 for Gears of War and Uncharted.
Wait, what?
I don't believe anyone would agree with what I just said. So, unless you mean to imply that 2D sidescrollers in general are somehow not worth as much as other genres, the OP makes absolutely no sense. Nintendo's continued success in this area is evidence that people find their prices fair, and the developers behind Trine and Limbo would absolutely love to sell their games for $50 or $60. The problem is, no one would buy those particular titles at that price.
And before anyone accuses me of bias toward one price/format/whatever else, I recently purchased both New Super Mario Bros U and Trine 2: Director's Cut, thoroughly enjoyed both, and thought they both provided great value for their prices.