Yes, that was me. Can't believe I even need to explain this...
Drag is paramount when it comes to time trialling (and let's be honest, most triathletes are just TTers with commitment issues). Take a look at the Ventum thread and you'll see that that there are a lot of people waiting for qualitative data in the hopes that this frame might save 50gms of drag. In fact, pretty much every thread involving bikes espouses the benefit of a lower CdA over things like weight and aesthetics. Speed is what is important, and disc brakes are detrimental to this pursuit. TriRig has built a massive following upon brakes that don't actually stop (naturally they've gotten much better, but still aren't a patch on DA) because they reduce drag. It's hardly a surprising trend as fiddly, spongy, and downright diabolical brakes are now a staple on TT/Tri bikes. Clearly in terms of drag disc brakes will always lose (Culprit data below), so what else to they offer?
http://road.cc/...-which-are-more-aero Disc brakes allow you to stop faster thus saving time on technical courses - Obvious triathlete bike-handling jokes aside, this is an obvious red herring. The number of courses in the world where any semi-competent cyclist would see the benefit over the drop in CdA is minute. If you're talking about Johnny Chopper with more dollars than sense and the skills that match Froome's composure, then maybe there are a couple more.
Discs would allow for more a aero design - Errr... no. There's still a giant disc and caliper in the way. Triathletes don't have to deal with UCI restrictions and yet the top tri bikes are only faster than the top UCI legal bikes at greater yaw where the bolted on bits (greater than 3:1) give an advantage. If you want properly innovative design then look at what Rafael have done with single sided forks and drum brakes (
http://vonrafael.com/rafael-r-023-2/).
Discs are the future - Not really. They're just fashionable at the moment as manufacturers are always looking to increase their profits (by selling us crap we don't need). Pros and their teams are not excited for disc brakes. Quite the opposite in fact. Will you see discs on a TT bike? No. This isn't a clincher vs. tub debate, this is aero vs. let's add a Pep Boys spoiler to a Civic debate. If ever TT/Tri frames become a thing, you still have the problem of wheels. A disc with a disc? Really? I wonder who will be the first to develop that...
So yeah, like I said. Honestly...