Well, technically this isn't correct. Don't forget about the Dura Ace wheelsets and higher end Campy hubs we discussed not long ago that have the flexible, plastic bearing retainers. So these would be cup and cone, but not "loose."

To the OP, the term should really be "cartridge" bearings, not "sealed" bearings. Lots of cup and cone bearings are considered "sealed" (although some are better than others). I've got old hubs that are actually labeled "sealed bearing hubs" and they're simply cup and cone hubs with seals. Shimano's mtb hubs, which are of course cup and cone, are from my experience sealed very, very well-