There is a significant difference. Being that a true AWD vehicle is designed to be driven on hard surfaces with all wheels getting power all the time. Most 4x4s will tell you in your manual not to use 4 wheel drive on Hard Surfaces. The power distribution to the wheels is different in Offroad 4x4 than in a AWD T-case.
Running 4 high, all the time on hard surface will cause premature wear on mechanical parts and eventually premature drivetrain failure. [Acceptions where noted by manufacture of course]
My Ford Expedition is a good example of an exception. Becuase its a completely computer controlled vehicle I have a 2H, AWD, 4H, 4L, settings for my T-Case. I use awd all the time. The manual states to never use 4H on hard surfaces for the reasons stated above.
This is why vehicles like Jeeps are listed as a 4wd vehicle and not AWD. The statement could be made that a Jeep is a Offroad AWD vehicle