Red/Blue and Fire Red/Leaf Green were two generations apart, along with Silver/Gold and Soul Silver/Some Gold.
Also:
Red -> Fire Red was Gameboy Phat -> GBA a technical leap of two consoles.
Gold -> HeartGold was Gameboy Color -> DS a technical leap of two consoles.
Ruby -> Ruby Remix.... GBA -> 3DS? Not sure how Pokemon would benefit from 3D, and Ruby still looks quite good unlike Red/Gold.
I dunno why people clamor for unnecessary remakes all the time, I guess the DS really does print money. :shakehead: