For what it's worth, if I'm going to be mostly indoors and in the car, I don't always wear a heavy jacket (or a sweater underneath my jacket) even when it's very cold out. There's no point in doing so if I'm just going from my front door to the car, and then from the warm car again to inside a building. So I don't find it strange that her jacket wasn't warm enough to wear in very cold weather.
The multi-layer jackets like DS's (I have a similar one) can get very warm very fast if they have all the layers intact. I reserve mine for times when I'm going to be outdoors for a longer period of time as it gets much too warm for commuting or shopping.
Lightweight tops tend not to have zippers; they're often used on clothes made of heavier knits and sweaters. I don't know but would guess many zip-up tops would probably be warm enough on a cold day, especially under a jacket.
So, I think it appears DS was dressed for going to work and back, but not necessarily for braving the elements. JMO