Yeah I think that's the point to them Karin. Those skimmers have a dedicated pump like JT said that chop and rechop the air, so you can get a large volume of microbubbles. Some units have multiple dedicated RC pumps, so the amount of microbubbles increases exponentially. If Greenmako still has his pics up, he had a deltec that had 3 or 4 pumps just to recirculate the water within the contact chamber. But, they set you back some serious cash.

Side note, Gabe has an injection skimmer on his main coral tank in the back, if you want to take a look at a working model.