Darkness you can solve. Taillights and brake lights are now available at such a brightness that you're much more visible at night than during the day. I'm seeing these more and more, too. Ice... is not something you wanna deal with on a bicycle. Period. I would go as far as saying rain isn't worth dealing with either unless it's a part of your regular. Dealing with rain means fenders and wet gear and washing the bike every day.
yah... I''ll ride in the rain - I don't mind it at all. But I haven't done ice/snow since I was a kid and learned that hard way that bikes and ice don't mix. And honestly - my last commute was better at night - more trails, very little on surface streets. My current commute is just a few too many miles on not-so-bike-friendly streets to begin with, in broad daylight. I don't need to ride... so I only ride when I feel safe. Even as a conscientious driver - during the winter when it's dark, it's just really damn difficult to see a bicyclist - even when they're lit up like they're at burning man.