Well, according to [http://en.wikipedia.org/wiki/Music_Production_Center|Wikipedia] it's a [http://www.ifixit.com/Device/Musical_Instrument|musical instrument], but it has buttons like an [http://www.ifixit.com/Device/Electronic_Keyboard|electronic keyboard]. So I put it there.
But you're right, it's a bit interesting. We should probably have a MIDI Instrument category at some point, or maybe we'll have enough of these things we can have a Music Production Center category someday. I think it's important not to categorize devices too far up in the hierarchy—it would really confuse newcomers to see an MPC2000XL next to a 'Microphone' or 'Electronic Keyboard' category. That's why I went with Electronic Keyboard.
