It's extra romantic seen as how Misty was Ash's first traveling companion and close friend. There's a unique bond there just like your first Pokemon.^ That's only in the manga, though. In the anime, she's the same age as Ash, just like May and Dawn.
And you do have a point, but you can't say that Ash has had the same amount of moments that could considered shippy. I guess it's all a matter of opinion, but I honestly think Pokeshipping is the one Ash ship with a chance of becoming canon.