everything that i have read on the subject, which has been considerable because i just got a brand new gen 4 17 with a USA made stamp, has said that there is no practical difference. Just the stamp is different.
on a technical note, my understanding is that instead of the traditional Glock finish, all USA models now have a melanite finish on the slide and barrel due to the fact that the finish used in on the austrian made ones produce cyanide as a byproduct.
i also understand that melanite is superior as it treats the metal on a molecular level, as opposed to just coating it (don't quote me on that part though).