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@The_Seldom_Killer
From the ocassionally interesting http://kentsbike.blogspot.com/
Michael, here's why the fixed on ice is NOT THE SAME as a single speed. First off let's assume that you actually never do coast your single speed. That makes you absolutely unique on the planet, BTW and leads to the question of why you bother lugging a freewheel mechanism along in the first place. But let's say you do that. Now let's take the case of deceleration, also known as slowing down. You can only slow by applying your rim or disk brakes. In both cases, the mechanism is the same, pads that interface with a rotating surface. Since brakes don't just stop you instantly (you wouldn't want them too!), the brake pads slide along the rotating surface. You increase and decrease pressure to control your velocity.
But (and this is the important thing) you have no way of knowing what slip you are getting comes from the pad/rim interface or the tire/road interface. So you think "hmm, I'm not slowing fast enough, maybe I'll squeeze the brakes more. If the slip is in the pad/rim interface, that will slow you more but if the slip is in the tire/road interface, you worsen your skid.
On the fixed, much of your velocity modulation is via your legs. Even when you use your other brakes, you get the feedback of your legs together with the action of the other brakes. This lets you do the same kind of calculation a modern automobile does when applying its anti-lock brakes, comparing the rotating speed of the wheel with the braking inputs to determine if a wheel is skidding. On a fixed gear bicycle, your brain can do this automatically, in real time. On a coasting bike, you don't have the data to do this calculation.
While slips and skids are most common in deceleration, they can also occur on acceleration. Wouldn't a freewheel and fixed be equal there? Nope. Even a very tightly engaging freewheel mechanism (say a Chris King) will have a bit of slop before it engages. Fixed gear bikes also are never perfect and have a bit of slop but it's almost always less than the slop in a freewheel. And when pulling out from a stop, it's hard to tell if the slip you are getting is from slop in the drivetrain or the tire slipping on the road. Minimizing drivetrain slip makes road slip more noticeable.
Finally, in sub-freezing conditions, freewheels sometimes become sluggish in having their pawls engage. Back in Minnesota every winter I'd see freewheel pawls freeze, making the freewheel spin freely in both directions. Running light lube in the mechanism and keeping water out usually prevents this, as does warming the freewheel/freehub above freezing but fixed gear drive-trains are immune to this particular problem.