From this post, I get the feeling you are under the impression that this is an abnormal occurance. Fair enough, it doesn't happen all the time - but I see T+ at a lower price than T often enough that I don't flinch anymore when I see this (especially on transborder routes). If you do a search in this forum, you will find a few threads. I've never actually seen the value in a Tango fare, to be honest, and I've never bought one - everytime I've looked back to the history of Tango fares, buying one plus a seat selection would have been the same as a T+.