It's not abotu a weird fetish, it's about what GF does. Until now, Pikachu's always been there Pre-National. Why would they change that? Pikachu is the iconic Pokemon that has been in every generation since the first one. It's not a Zubat or some unknown (albeit useless) Pokemon. It's the mst well known Pokemon there is.
Technically, in G/S, you can't get it until after you beat the Elite Four, as it's only found in Kanto. I can easily see them having no existing Pokémon until the National Dex is unlocked.