Back in gen 1/2, Pokemon characters were drawn in a unique, iconic art style. Look at the Ethan's original artwork for example:
http://cdn.bulbagarden.net/upload/a/a3/Gold_Silver_Ethan.pngThe washed out colors and rigid lines gave Pokemon characters a unique look. Even if you didn't know Ethan was a Pokemon character, you'd recognize that Ethan couldn 't possibly belong to any other series as long as you were somewhat familiar with the Pokemon art style.
And then in gen 3, Game Freak trashed the old art style and replaced it with a generic kawaii moe style. Nowadays it's impossible to distinguish Pokemon characters from your standard desu-game characters.
Look at HG/SS Ethan, redrawn in the gen 3/4/5 desu-style:
http://cdn.bulbagarden.net/upload/thumb/c/c0/HeartGold_SoulSilver_Ethan.png/303px-HeartGold_SoulSilver_Ethan.pngAs you can see, Ethan has been rendered a generic moeblob. You could literally insert New Ethan into an episode of Lucky Star or K-On and nobody would bat an eyelid, because it's the exact same style.
