Fallacy. I've been riding fixed on the road with QR hubs since 1974. A wheel with a fixed cog will no more slip than one with a freewheel or cassette. And even if the QR is not tight enough, you'll never rip a wheel out of a track end; the opening points the wrong way. I've yet to rip out a wheel on forward-facing road dropouts.

On the track, where you're required to use track nuts, guys will usually pull the wheel on a kilo start, if they pull it at all. The worst that happens is the tire starts rubbing on the stay. If the rider crashes, it's only because he's taking a dive in order to get a restart (the rule used to be that you only got a restart for a mechanical failure or a crash, and a pulled wheel didn't qualify you for a restart. I think that now they've changed it so that you get one restart).

Anyway, on the road, a QR makes it way easier to line up the back wheel than track nuts (track nuts you set up one side at a time; QR lets you set up both sides of the axle at once). I have never understood why they only sell wheels for road fixies (clincher wheels) with track nuts (and the track nuts are usually the cheap one-piece nuts, not the nice pro type with built-in washer). I always end up having to replace the axle with a hollow one and cutting it to size with a Dremel cutting wheel since the shortest hollow axle size is for 126 dropouts if you can find them. Another example of the bike industry not having a clue...

Luis