OU beat two non-conference teams that ended up winning their division, one of which is in a BCS bowl. They also thumped TTU and beat OSU as soundly if not better than UT. OU also lost earlier in the season, which like it or not is a big detail.
Obviously it's not a perfect system, but I think UT can only complain so much about not going. If they could have played a shred of defense against TT in the 4th quarter, we wouldn't be having this discussion.