hey beardking, I can try and explain as its my quote.
A 73 degree seat angle with low bars results in a closed hip angle and reduction in power.
First, the UCI isn't logical, that is why its their rule. And remember the rule is not a 73 degree STA, its a saddle that is 5cm behind the BB unless you get a morphological exemption. So it means shorter guys are forced to ride effectively slacker seat tube angles. A tall guy can ride close to an effective 76 degree STA with a saddle 5cm behind BB. Levi Leipheimer gets an exemption and rides about 2cm behind the bb.
So, like I said, pro Time Trialists typically ride more forward than 73 degrees, look at Taylor Phinney in 2012 for instance:
http://www.cyclingnews.com/news/photos/ ... ial/188907" onclick="window.open(this.href);return false;
as compared with 2008 where he is clearly more around 73-75 degrees:
http://cyclingresults.wordpress.com/200 ... onatthett/" onclick="window.open(this.href);return false;
He is clearly not in a 73 degree seat tube angle position in 2012, though a little closer in 2008. By 2012 Phinney had changed to using an ISM Adamo and therefore can sit on the end of the saddle and run an effective seat tube angle closer to76-78 degrees like many triathletes because he can run it 5cm rearward of the bb and sit very far forward.
As for being able to go fast despite the hip angle limitations, these guys go fast because they train around those limitations. Specificity and big engines overcomes a lot.
So as far as buying a bike goes, I would recommend buying a bike that when you need to you can get your saddle 5cm behind the BB. If that race is important to you, I would recommend finding a saddle that allows you to use that position enough to be good in it.