i believe its true, unless a few hundred studies conducted were all false (i made that up i dont really know how many there have been). From what i know, and i may be incorrect, but the higher seatpost angle (usually from 73 degrees to 78) relieves tension off of the quadriceps which are the primary muscles used for running. Along with that, i think that the aero position is more comfortable with a larger seatpost angle. Those comments are from my personal experience as well (i´ve ridden both regular road bikes with aerobars and tri bikes with the 78 degree seatpost), and from what i remember everything felt a little more comfortable, plus my quads werent as tense after the ride when i was using a tri bike with a 78 degree seatpost angle (doesnt have to be 78, but it was in my case)

Agree with everything said above.
Go look at the geometry of road vs. TT bikes on some bike sites, usually its about a 5 degree difference, just like Gsal posted.

[b]Road bikes[/b]: The seat tube angle is generally 73 degrees and the rider’s position is often upright. [b]Tri-specific bike[/b] geometry has a steeper seat tube angle, usually 76-78 degrees. The head tube angle is usually a little less aggressive, the top tube is slightly shorter, and often the front end slopes.

And if you are a visual learner:

[img]http://www.bikesportmichigan.com/bikes/road-vs-tri/dia.gif[/img]

Road TT bikes also have to fit the UCI rules, while Tri TT bikes don't (that is why the different saddle options on many TT bikes).