My opinion is that the oil bath bearings, as far as lubrication is concerned, are superior to the grease-packed bearings. The complaint about oil-bath bearings is that they can sometimes be a little messy - if I'm on a trip where I've given the disc brakes a good workout, I may have some streaking on a random wheel. The high temperatures generated by the disc brakes will sometimes push a tiny bit of oil around a hub cover o-ring or rubber fill plug, and this tiny bit of oil will pick up brake dust and make some black streaks on the nice, shiny aluminum wheel.
To me, this is no big deal. I routinely check the oil in my hubs and have yet to add any, so any oil loss is insignificant. I'll just wipe down the wheel and go on. To some other owners, however, having to clean a wheel every now and then seems to be a HUGE deal - thus, the change back to grease-packed bearings.
Edit: DRV will supply a kit to change the oil bath to grease-packed bearings. It consists of hub covers and new seals. I suppose one could change the other direction from grease-packed to oil bath with the appropriate covers (with o-rings & fill plugs) and seals if desired.
Rusty