They made a new Earthbound (or rather, a new Mother game, called Mother 3) a few years ago for the Game Boy Advance, but only in Japan. However, they might do something to rectify that, especially now that Lucas (the hero of the game) is in SSBB. That could potentially mean a GBA release, DS, or even VC/Wiiware.
As for Earthbound itself, I still think they just haven't got around to it. Here's hoping they bring it out for Europe.