I seem to remember in one of the games Elm mentioning the last starter being stored for safekeeping to prevent the issue with the rival/antagonist person (Official name plz?) from happening again. I still haven't actually started playing HeartGold, so I could check, if I weren't lazy, and preferred the color silver. Although it would be rather interesting if Nintendo had you play as one of the unknown characters that kind of grabbed the remaining starter and played through the game, but with all of the events completing just before you got to them, and then having other issues arise because of such. But that's another topic :PP