When a lawn is very dry, or if there is a very heavy thatch layer, aerators don't tend to work very well. The tines penetrate into the soil, but they don't pull the plugs out of the ground (I'm not sure why this happens, but it does).
Sure, you could simply water your lawn regularly like you're supposed to, or power rake the thatch layer out, but that's too practical, dammit!
What is needed is a very complex system of little claws at the end of each tine, so after the tines penetrate, the little claws clamp shut around the bottom of the plug, physically ripping it out regardless of how thick the thatch layer or how dry the soil may be. Once out of the ground, the claw opens again, preparing for the next penetration.-- 21 Quest, May 14 2007halfbakery