There are different approaches to this problem. What kills your bike in the winter is mostly salt, a little bit grit (eats your drive train). Really cold temps are pretty safe for your bike, but the damage happens when it gets above zero (or a little below zero when the salt melts the snow into slush). You can just deal with the damage that happens, or you can actively work to prevent it.
Either:
1. You get a crappy bike, just ride it through the winter and have it pretty much disintegrate come spring (cables will rust and stick, derailleurs will stop working, brakes will rust and stick)
2. You get an OK bike. You take apart the axles, the derailleurs, the headset, brake pivots, the bottom bracket and grease them all with waterproof grease (marine bearing grease works well, as does snowmobile grease). Then after every winter ride (if commuting after every time you get home) you pour boiling hot water over the bike to knock the salt off and give it a quick wipe down, re-lube the chain and brake pivots, and maybe occasionally do some re-greasing. I've managed to get a bike to last through five winters of commuting by doing this.
There's also
3. Get a an IGH bike with a belt drive. It's more expensive but will require less maintenance.
4. Get a fixie. It sucks if you have any hills, but will require less maintenance.