^Also Naoko at the time was a complete newbie to manga really. Its a lot easier to recycle character designs than have to create them. I'm also sure she had a lot of direction from say her editor and what not.

^I totally agree. My sister is an animation major, but before that she was in illustration in high school. If you look through her earlier sketchbooks, almost every character, OC or fanart, looked the same. Now that she's got a few more years under her belt, they share some basic traits but still look individual. In some of naoko's later works, like toki mecha and Witches wish, they don't look so much as clones.

You can tell with a lot of artists that they recycle character designs, and as Cosmos said, this tends to happen more in the beginning.

I think it's easier to get one style down and then diversify from there.