But graphical improvements do occur!
Here are the six main Pokémon games. See how they've evolved...
1998: Pokémon Red/Blue on the Game Boy starts simple
Still via PokemonDungeonTV
2000: The Game Boy Colour gives Pokémon Gold/Silver gives the series... colour.
Still via Chuggaaconroy
2003: A major font-kerning upgrade appears in Pokémon Ruby/Sapphire, on the Game Boy Advance.
Still via JakeTheHappySnake
2007: The Nintendo DS, uh, barely improves things. Thanks for nothing, Pokémon Diamond/Pearl.
Still via PokeGuideHD
2011: That's better, Nintendo DS! Pokémon Black/White have appreciably better graphics.
Still via PokemonJourneyHD