When the popularity mutates it, yeah.
Take a celebrity - he starts off producing great music, and doesn't really care about the money or fame, but likes singing. Then people start to recognise him and buy his albums. Suddenly he's selling illions and billions of albums and singles. Then he forgets what he actually is doing and produces slop because he knows he'll get money because he has a contract or whatever.
Pikachu is just like him, everyone knows him and he's actually become sort of a celbrity - got skinnier, taller, more plastic less chubbier. Not as cute.
Pichu is hardly ever seen as Pichu now, only as Spiky-eared Pichu or Shiny Pichu.
Wow I take things seriously XD