I consider it similar to how Saban zoned in on the Tai/Sora pairing in Digimon when in actuality, it was Matt/Sora. The problem was, it was too subtle in the original Japanese to where even the voice actors expressed surprise Sora ended up with Matt. This was done to subvert the expectations that the main girl would fall for the main hero and not the lone wolf.
I do believe in the original there was chemistry between Ash and Misty just because the animation shows it. The voice actors cemented that further, however; as I've not watched much of the original subbed, I'm going off the assumption the original Japanese voice actors worked off each other very well likewise how Veronica Taylor and Rachel Lillis worked off each other well as the characters. I don't know why 4KIDS insisted they were an item (albeit one-sided, Ash was always portrayed as oblivious), but I think it was honestly inevitable that we'd get your PokeShippers, and your PalletShippers, and your OrangeShippers, et cetera, et cetera.
RocketShipping is all but officially/explicitly confirmed, so if you're looking for some kind of romance in Pokemon (prior to XY), that was your go-to pairing. Though funnily enough, I don't think 4KIDS pushed Jessie/James as much as they did Ash/Misty. Just kinda something I've noticed.