I did used to keep a car and sometimes I'd be lying in bed thinking how cold and dark it is outside and I could have another 30 mins in my bunk.
A few years ago the water pump broke and I didn't bother mending it.
This meant I didn't have the option of using the car. I got a second Brompton to cover inevitable technical problems. One year of no VED and insurance covered a lot of the cost.
Since then the only day I haven't used a bike for getting to work was in January 2009 when I had to pick someone up from the airport after work.
I keep different tyres on different machines because they have different uses. Ice isn't a big deal on a trike. Camber is interesting but ice is fine.
OK, that rambled a bit. I think the bottom line is that I don't have an option. I have to use a bike to get to work so I do.