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I'm sure I've read somewhere that the bearings on all of these don't have seals which might explain the spinniness but I guess you have to be prepared to replace them with some that do at some point.
Kanj-
I've read somewhere that the bearings on all of these don't have seals
That's where 99% of the gain comes from, particularly in dérailleur pulleys where seal drag is the dominant factor. Ceramic bearings don't need need liquid lubricant kept in by seals, and they don't need water and solid contaminants kept out. Almost everything which can get in is softer than the bearings and is either ejected whole or crushed to powder.
That's for full ceramics, especially ZrO2. Of course, a lot of cheap "ceramic" bearings sold to cyclists are hybrid units with Silicon Nitride balls running in ordinary steel races.
gbj_tester
Bearings spin a lot faster, but under load I can't tell any difference.