Even up here in the tundra, where it rarely goes above 80F, wearing my work clothes on my commute doesn't work for me because I treat my commute like a time trial. Heck, I sweat too much to wear work clothes on my bike even when it's only 60. That said, for only 10 miles each way, I don't bother kitting up either. Cotton shorts and t-shirt work just fine for me. Ride how you want, wear what you want, and don't worry what someone else is doing.