canklecat : I apologize for not being clearer and more complete in my response, and I thank you for correcting me. Yes, some tools are required for bearing replacement on DTS hubs - but that will be true of most (perhaps all?) sealed cartridge bearing hubs. What I meant (and I should have been clear) is that a ride-ending freehub failure can be handled in the field without tools, as the star ratchet can be replaced with bare hands. (I don't carry a spare, but I have read about mtb riders who carry them on rides in case of failure.) I don't know of any hubs that allow an easy field replacement of bearings, and I don't know why anyone would ever even need to do that.
My oldest set of sealed bearings hubs are 12+ years old and have never needed service, so I regard them as virtually maintenance-free. While they may need bearing replacement someday, it's conceivable that I will never have to open them up. But who knows?
I do agree with you about old school cup & cone hubs: they are easily serviced with an inexpensive set of cone wrenches. As an added benefit, I have found that even my cheapest, nastiest, no-name Taiwanese hubs are incredibly smooth as long as they get an occasional overhaul with fresh grade 25 hubs and a big load of Phil Wood grease. However, I don't enjoy servicing them, and so I prefer sealed cartridge bearings.