And some games just had little extra features if you used one of the extra buttons (Boogerman exclaims, "Booger!" if you hit an extra button, IIRC). Hell, the Sega Genesis even had a portable version of itself. You could also buy the Power Base Converter and have backwards compatibility for the Sega Master System. There's also the Sega CD and 32X... which are a bit gimmicky, but did have good titles like Knuckles' Chaotix, Star Wars Arcade, and Virtua Fighter. The only comparison we get from Super NES is the Super Game Boy attachment -- for playing Game Boy games on the Super NES. That's kind of boring, especially since the point of a Game Boy is mobile/handheld gaming.