I've heard this over and over, but I never quite understood it. My commuter/snow bike for the past few years was an old Trek set up with 'cross drops, a 1x7 friction shift drivetrain (which I really miss), and 38c tires with knobs on the corners (not my choice, but they came on the bike and the whole thing cost about as much as a set of tires). Despite not being fixed, I can't imagine ever having my rear wheel spinning without my noticing. Accelerating from a stop is pretty much the same no matter what you're riding: If you apply too much torque, you feel it slip. I can't see how this could be different on a fixed gear, a singlespeed, or a 27-speed tandem recumbent tallbike.

What I could understand is feeling your tire start to slide laterally while turning, though I've never ridden fixed in winter conditions.