I've imagined that the electricity Pikachu's absorbed is what set him apart from other Pikachu. It's amped up his strength in many ways compared to most Pikachu, and the fact Ash's training him has made him stronger, even if he does get debilitated a lot of times in the beginning of each new saga, but I chalk it up to some bad writing tactics even with Pikachu's experience. Sure, Levels aren't used supposedly in the anime, but it still is a bother. Anyhow, I've often beleived from the times Pikachu's absorbed electricity that he's gained power from it; from absorbing that electricity from Misty's bike and all those Pikachu at the Viridian City Pokémon Center as well as when Flint helped him and Ash get ready for a rematch with Brock and other times too.
"Looks like you're about to get pwned."
I don't care about EVs. If you don't either, copy and paste this into your sig. (Started by Shiny Metagross)