In Japan, there are shows where males play all the parts, including females. It's called Kabuki theatre and is a sort of tradition. Jessie and James are constantly putting on costumes and this must be a "tribute" to Kabuki, right?
For example, in the St. Anne Jessie and James dressed up as girls. They had to fool Ash-tachi into going on the ship. Now if James was disguised as a guy the whole plan wouldn't have worked cause Jessie says that the reason they can't go on the ship is because 'we have to, like, go out with our boyfriends'.
Another example is the Officer Jenny episode. Jessie and James dress up as Officer Jenny to get the Growlithe to listen to them. Since there don't seem to be any guy police officers, dressing up as a male policeman would've made absolutely no sense. The plan wouldn't work because, obviously, the police Growlithe would see that James was not an Officer Jenny.
Now I know there are some parts where Jessie is the guy and James is the girl. The people who made Pokémon probably thought it would be funny. I mean, the little kids who watch the show were probably laughing hysterically at those parts. I happen to think it's kind of cute.
And remember what I wrote in the Rocketshipper section? About how almost everyone has crossdressed at least once, even out favorite Pokémon master wanna-be, Ash(ley) Ketchum. It's just a way of life in Pokemon-world.
I've noticed lately in the Johto/Ho-en region episodes that James hardly cross-dresses anymore. Might have just been something the creators were "trying-out".
