Riding in nice office/casual clothes?
Those people you mentioned seeing in 'office clothing' most likely don't have a very long commute. Depending on where you live it may be like here in Switzerland; it has become some kind of trend. People show off their dutch style bicycles and feel awfully cool, which might explain why you perceive them as looking like fashion models. You will also notice how many young and trendy guys ride a women's bike because they idealize the authentic dutch hippie bike. I just pass by and smile at their confusion regarding bicycles.

For my part I ride ~ 10km to work on my old Batavus Champion, in every season. A little perspiration is normal, but I don't really need to change clothes when I arrive. 

I think the key to successful commuting over longer distance is having an exceptionally good deodorant.