Holy crap, I didnt even know there was a GB one. Was it good?? Screw it, ill just order it and find out myself worst case scenario i wasted 12 bucks. I think Ninty is hoping that the exposure in Brawl will help push Kid Icarus into the limelight. IT kinda worked for Fire Emblem with Marth and Roy in Melee??
I think it's more that a Kid Icarus comeback was frequently requested by diehard Nintendo fans during the "Nintendo has gone all casual!!!!!111" era (most especially by IGN). E3 2010 centered all around old Nintendo heroes like Donkey Kong and Kirby returning (plus Goldeneye), so KI fits right into that mix of Nintendo trying to appeal to a certain segment of their fanbase.
The exposure theory doesn't make that much sense, because for that Kid Icarus is coming too late (four years after SSBB), Ness has been in SSB since the beginning and Mother 3 still didn't release outside of Japan and lastly, the Fire Emblem characters were deliberate choices, because the corresponding games released around the same time as SSBM (Roy in Fire Emblem 6 in 2002, although not released outside of Japan) and SSBB (Marth in FE1 remake, released in 2008 in Japan and Europe, early 2009 in America).