I need backwards compatibility because eventually my old system will break, like what happened with my Gamecube and Xbox. The Gamecube has the additional problem of having external memory that just loves to go corrupt after a year or two. Actually, I'm not even sure that my Gamecube broke, I think I just preferred being able to play Gamecube games on the Wii, since the memory card was already shot and all.
But to answer OP's implied question...I keep my old systems for nostalgic purposes and also because they have my saves on them (for Xbox, Xbox 360), and because "why the fuck not?" Backwards-compatibility is absolutely essential, though, because old systems tend to break pretty easily.