My take on the subject as a former all year, all weather commuter, come sun, rain, slush and snow.
I did use my former good bike (at that time it was a year old) during one winter. In the following spring I found exactly what Yellow Saddle described, rusting bolts, springs...not in itself terrible but a little disheartening. Worse was the furring corrosion building up where the paint chipped off the ally frame...again, fixable but disheartening on a relatively new bike.
Worse still was finding the paint and or carbon peeling off the alloy head of my carbon /alloy forks . Corrosion obviously started in the brake caliper holes and worked it's way down. Not structural but not pleasing either.
That wasn't even a particually wet winter at that time, just residual salt for the most part.
I admit perhaps better attention to frame cleaning might have helped, but I don't abuse my bikes either,
Winter bike for me after that.