Just some refining points to make. Hollowtech (I) were cranks designed for the octalink cartridge bb interface. Hollowtech (II) is the external bearing type. When you talk about Shimano groups, it's best to be specific with the model number, not just the general group name. XT, for example, has existed as square taper, octalink and external bearing type cranks/bbs. Shimano trickles the technology down normally after introduction at the XTR level, then to XT, to LX/SLX, etc. If you're curious about the timeline of various Shimano introductions, try this http://www.mombat.org/Shimano.htm

Another point on octalink bb's is that the better ones are no longer being made available as Shimano has focused it's new stuff to be the external type (for now at least), just as they did with their better square tapers when switching everything over to octalink...