Nah, Shimano hubs are all about the same really. Good Shimano hubs all have contact seals and boron hardened cones. I've got LX cones in my 105 hubs right now, so how much difference could there be?
I'm pretty sure Shinamo could make just one line of hubs and set a standard rear spacing for all bikes and things would be a whole lot more simple. But then Shimano isn't really into making things simple, they do business for $$$$. And having 2 lines oh hubs, MTB and road, helps sell more product.
BTW, the new 2007 Tiagra hubs look a whole lot like the older Ultegra hubs a few years ago (Shimano uses trickle down technology all the time) I haven't taken one apart to look that how smooth the cones are, but I've adjusted new wheels build around them and they seem to spin smoothly enough. I'd trust them to tour with.