The massive heat sinks are to keep the LED operating temperatures lower, which radically extends their service lifetime. Cree claims 50,000 service hours for their current fixtures.

I bought a bunch of Cree LR6 lights ($70/ea. online) to replace 60W halogen ceiling lights. They consume only 10.5W and put out light that looks damn near identical. Comparably bright CFL bulbs, in warm white but with lower CRI, seem to clock in at 15-20W.

One of the real winning features of the Cree lights, relative to CFLs, is that they're instant on. No warm-up period. Another feature is that you don't hear anything. Where I have CFL bulbs in our house, I can hear their power transformers quietly humming away, which bugs me a bit.