US Glocks have the same finish as Austrian ones. I have both. The finish you see is not indicative of the hardening process, though.
Best I can tell, Glock quit using Tennifer (a trademark name for the hardening process) some time ago. You won't find it in any of their literature like you used to. Their new process is still some manner of nitrocarburizing, from what I have read, it just isn't the Tennifer process.
In any case, you won't notice a difference if US Glocks have a different hardening process, and they've been pretty consistent with their finishes as of late, so it really doesn't matter. Bud's is full of it if they're charging an additional $20 for US-made Glocks.... I bought mine locally for $0 more than the Austrian ones.