Hehehehe, actually, Clefairy was the intended mascot for the franchise before for whatever reason Pikachu became more popular, so out came the white angel and in came the yellow rat. (Porygon was at the lower tier of the pokes, matched with Tangella, Ditto, and all those other "gimmics", and it completely lost any note in the anime when Pikachu induced seizures in its episode. )
And yea, I understand what you're saying, some pokémon simply cannot be changed like Electrode or Ditto, but Porygon2 was actually the result of the concept of sub-division in 3D graphics (don't know where the neck came from though.), and a "cutified" version of Porygon can be seen in Pokéranch, which resulted in making it's head bigger the the rest of it's body...
But we've strayed too far from the topic...