I was just browsing through the TT bike thread and I was wondering, why do they all (almost) have weird looking big dorky saddles ? what makes a good TT saddle compare to a road bike saddle ?

Lots of people are riding Adamo/Cobb type noseless saddles. Essentially, they allow for you to "roll" your hips forward more. This allows a more aerodynamic position with less crotch discomfort.

Most of these saddles have two prongs that sit under your sit bones and then a big gap for your soft tissues.

I'm on a Performance Bike tt/tri saddle as I found the adamo to be too wide in the prongs. One drawback of a normal saddle even with a cutout is that your junk rests on the nose; instead of just kind of free hanging. But most of the circulation benefits seems to be maintained with a good cutout.

Well, for the noseless (or "2 noses" saddle), I understand. But there is another one, very short and big compare to the normal road bike saddle which are flatter and longer...

Do you have a picture that'll help illustrate this? Not very clear what you mean.

Could just be angle of photos. Or possibly he is referring to a Dash Tri.7 saddle. I have the longer TT 9 but point has already been made about purpose - sit on sit bones and rotate hips forward, which enables super aero position with least amount of discomfort (crotch and breathing) which enables maximum sustainable power generation.

The less nose the more positional choices you have while staying UCI (5cm behind BB) legal.

Because the UCI only lets you have the saddle within 5cm of the center of the bb. Which is a stupid rule that applies to a 5' rider and a 6'8" rider equally. So, in order for a professional rider to get the position he needs to do his best in a UCI (Ultimate Cycling Idiots) race he has to call in the engineers and they have to pay for a special saddle that no real human would ever buy.

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For certain parts stiffer is more important than lighter.

Im on a Dash Stage 9. Weird looking mofo, but the best move I have made in terms of comfort. My TT times actually got faster with this thing because I quit moving around and thinking to myself how uncomfortable I was.