Again with the UCI/non-UCI differences, but since Tri bikes don't have to conform, there are a lot more possible frame combinations.
A Kestrel Airfoil
A Softride
Plenty of pro triathletes and some age-groupers ride their bikes in very, very good aero positions:
Torbjorn Sindballe, Craig Alexander, Norman Stadler... see
some examples here.
While I wouldn't want to think what would happen to me if I tried to race some of those positions for 100+ miles at a time, that isn't to say that there aren't athletes who do amazing things on the bike.
However- The thing to keep in mind during a tri... "bike for flash, run for cash"
It always comes down to the run, if you can't run after the bike than you can't win- and that is what drives some bikes to be
setup with a little more comfort in mind. Most bikes can be used in a huge range of positions- your hard-points and personal preferences are what make the difference.