You can, but cutting the top off the bulb makes it easier to get the cloves out when it's done.
I tend to not cut them straight across, because you lose a lot of garlic that way. I cut them angled downward from the pole to the fattest side, so that it exposes the cloves and I lose less roasted garlic goodness that way.
I loosely wrap them in foil too, as it seems to keep the garlic from drying out.
If I had to guess, they're doing something like what bonfire recommends, but using peeled cloves, and a very, very low oil temp.
[This message has been edited by HTownAg98 (edited 5/24/2012 2:01p).]