NO Otterbox for Galaxy S II
I think the problem is that a lot of people buy those samsungs because they are so sleek and slim, and usually have pretty durable screens on the front. And putting an otterbox detracts from the looks and thin-ness of the phone. And with gorilla glass, there is no need for the plastic over the front.
I understand your assessment however there is an Otterbox case for both the International and AT&T version. I wonder if Otterbox thought they would not have to make a T-Mobile version as the pending merger with T-Mobile was still on at the time of the phones U.S. release but the deal since fell apart.