I'd get too sweaty riding in my work clothes for a coat-and-tie professional office. My commute isn't extremely hilly, not constant climbing like riding a mountain pass, but still, 350 feet of climbing in just my first mile from the train station to the I-90 trail, then 5 miles of rolling hills... I break a good sweat doing that in under half an hour.

Since I need to change clothes anyway, I usually wear cycling clothes for the commute. They're more comfortable at that level of exercise, especially when it's raining. I have ridden plenty in jeans and a tee shirt, but if I'm trying to make good time on a rainy day, I'd much rather wear something more suitable that doesn't get heavy, wet, and cold.