Bråndeewine writes...

"Frank writes...
Why doesn't Elisa change her clothes?

Greg responds...

She has 102 black t-shirts. She changes three times a day.

Or were you looking for a real world answer? We couldn't afford to redesign her every episode. And the more different looks we gave her, the more we were inviting animation errors.

(No one mentions why Owen seems to wear the same suit every day?)"

The reason no one wonders about Owen is due to the fact, that we assume that he is so orderly that he has a suit for everyday that is identical. Think "The Fly" :oP