When you think of it even more closely, the personalities of the characters they are dressed as is practically identical. Well, maybe Miyuki isn't a flirt like Aeris, but still.
Random trivia time, Wendee lee, who did Konata's voice, also did the voice of Bulma in the obscure Harmony Gold dub of Dragon Ball (only 5 episodes and movies 1 and 3 were dubbed, and all the names were changed)