i think there is a type of game that sells on a nintendo handheld, but i don't believe consumers say 'oh, here's a game published by nintendo, i must buy it'. if that was the case why did ouendan, hamtaro and advance wars sell poorly in japan and why weren't super princess peach, kirby cc and yoshi touch n go really huge sellers?. in fact i'd go so far as to say many consumer think nintendo makes all the games on its hardware and sony does on theirs.
also nintendogs and brain training were new franchises and as such had no previous association with nintendo. they sold because they were good and from the weekly sales charts it's very clear word of mouth spread and spread until they became million+ sellers.
from the sales the psp has an audience, which is one that likes ps2 games, so from that perspective ds hasn't 'lost' anything that sold well on gba. the truth is non-japanese publishers have never invested much effort in nintendo handhelds other than movie/tv tie-ins and a few other kid friendly games. so, psp and ds are, surprisingly, living pretty separately and each is doing well. this is great, because it give consumers more choice and developers try harder to make the best games they can, which has been especially evident with nintendo.