It will depend on which version you are talking about.
For example, the original Asian releases, at least the Japanese version of GT4, has the old Mini in it and no other versions have it, including the GH versions.
Also, the GH version had a compatibility bug fixed so that it could work with an early version of the PS3 OS.
There were no major GH differences, though, unfortunately, because GT4 has so much that is incomplete, missing or rushed, but SONY doesn't want to have major differences between the same game versions.
Cheers,
MasterGT