Personally, I think Pokemon was originally intended to be like that, until Nintendo came into the picture. Now before you start to debate me, just know that I'm male and I'm a huge fan of NIS and Gust games (a majority of which were made for girls).
So onto the reason. Well, multiple reasons actually. First of all, you've got a bunch of male characters that are considered, as stated by many female fans, to be just plain adorable. You've got female characters that compete in these talent contests and a Pokemon verion of Westminster. Both of these things appeal to females, though I imagine the Westminster thing also appeals to males as well. Makes one wonder why there hasn't been a Pokemon Best in Show Fic yet.
Then there's the cuteness factor. Now, we know alot of guys have a soft spot for the little creatures, but females love things that are cute. Seriously, if you doubt me on this, show them your Pokemon plushie or beanie baby collection. Or better yet, show them your Tails plushie. Or even your cat. All of which are cute. Guaranteed 9 times out of 10, they'll love it.
I think that what happened is Game Freak probably thought of this and was originally going to market Pokemon to girls. But in what I'd consider to be a pretty smart move, they decided to just market it to kids in general when Nintendo bought the rights to the franchise. Which is really ironic when you consider that the Pokemon Anime still has the aforementioned appeal to it more than anything else (if not moreso now with the contests).
