ok, now you got me wasting time (I thought I could just leave this at "idiotic"). The whole point of a warmup is to get the blood flowing well enough to carry O2 and prevent massive lactic acid buildup in the early part of the race, which is what happens if you go out hard when cold. You want to minimize the amount of O2 debt that you go into early on.
I'm not really a runner, so I don't know what, say, Mo Farrah does for his warmup. But assuming runners follow endurance logic, a proper warmup involves bringing the cardiovascular system up to speed slowly. You want to move through all the zones to get the lactate-clearing mechanisms working, gradually.
The perfect warmup is different for everyone, because obviously an unfit individual can't do too strenuous a warmup without becoming exhausted. My preferred warmup includes 10-45min L1, 5-10min L2, 3x3min L2-3 (or some other form of easy intervals), 5-10min of 10s sprint, 50s rest. I work backwards so that I can finish this 10min before my start. For orienteering races, I'll frequently replace some of the L3 work with running drills, which jack my HR to L3 anyway, because I think getting the jumping/twisting/cutting muscles need to be warmed up for dashing through the woods. If I don't get in a full warmup, I adjust my starting pace of the race, because going out hard on a short warmup basically screws you for the rest of the race.
This article explains things pretty clearly.
Here's an article in a skiing journal about warmups.