The idea of different price points per generation is commonly thrown around, but yeah, you're right, whatever price a NES RPG like Final Fantasy is, you'd wonder if it ought to be the same price or considerably more than an early NES game like the three-stage NES Donkey Kong.
Prices per generation just seem like a good idea because games are typically more elaborate each generation, so it makes sense to the consumer, and cost more to make originally, so it makes sense to the developer. But it's an assumption more based on graphics than gameplay. If you had a long NES RPG and a short Super NES arcade-style game, which should be worth more? Which would be more fair to charge more for?
But if games end up being priced differently based on gameplay, who makes these decisions? Even if it's strictly by genre, you'd have to be sure what the genres are, and what to do about multi-genre games or games that defy genre. (I insist that The Legend Of Zelda games are adventure games and not RPGs...no one ever calls StarTropics an RPG and they're very similar...but many people disagree with me and insist on sticking Zelda with the more turn-based or stats/numbers-heavy RPGs.)
Even if you could get a general pricing plan that works, either by console or genre, there's bound to be somebody who'll disagree with the prices of particular games.