delperj,
I can't say what the structural differences are, but I can tell you some of the differences I've seen since owning the Elk Ridge and walking through the Big Horns at the RV show, plus comparing the features lists online:
BIG HORN HAS:
bigger freshwater tank
hydralic vs electric jacks
more residential lighting fixtures
more residential plumbing fixtures
more residential shower enclosure
More cabinetry in the bedroom, kitchen and bath
storage drawers in the steps
larger fridge
3 zone speakers vs 2 zone
heavier suspension
winterization valves in UDC
day/night shades (vs night shades only)
fancier slide out facias
larger storage basement with rubber floor (instead of carpet-like material)
heavier-duty power cable
molded rear cap
hydralic slides
I really don't regret not having any of the Big Horn features, but to each his own. We are not full-timing, we just have long-weekend and week-long trips when we can get away from our 2 full-time jobs. ;-D
Hope this helps!