I suspect the same, but not "unlocked vs locked", instead "T-Mobile oriented vs not" (there's a subtle difference) ... but right now there are only two available forms of Android (official consumer T-Mobile G1, and Google Developer G1), and as far as I know, both are tethering deficient. But both are T-Mobile oriented, even though the developer G1 is unlocked.

Until we see it on a different carrier, and/or delivered through a different partner, we wont know for sure if Google will be delivering different features to different carriers/partners.