Big differences in quality and design IMHO.
Take a look at materials used (real wood vs. fiberboard for example).
IFS vs. solid front axle (makes a difference when being passed by semi's and tour buses).
Protected and labeled wiring (vs. rat's nest of wiring found on some).
Side radiators vs. rear (if you want to keep your engine clean).
Generators on a slide vs. not (if you want to easily service your genny).
Properly terminated wiring (vs. any crimping tool the electrician happened to have in his tool belt).
Good acoustical and thermal insulation vs. insufficient.
Underpowered vs. sufficient power (displacement, torque, not HP).
The first time I went to an RV show, I was just like the OP....they all seemed the same.
Years later I made the purchase after realizing that they were indeed very different!