2009 tour de france green jersey

Why is it that some pro Tour riders still ride on the Dura Ace 7800 rather than the lighter and better 7900?
The Cervelo Test Team to be exact.
I was watching the TDF a few stages ago while Mark Cavendish was taking the sprint finish. Thor Hushovd had to stick to his wheel to keep the Green Jersey, when I looked at the photo, it looked liked he was using the 7800 shifters.
How I could tell? The 7900 finally featured hidden shifter cables while the older 7800 shows the shifter cables.
Look at Thor Hushovd (Green Jersey)
http://www.cyclingfans.net/images/2009_tour_de_france_mark_cavendish_columbia_htc_highroad_wins_stage19.jpg
This picture was taken just recently, while the 7900 was already released.
Hayden Roulston also looked like he was using the 7800.
http://www.cervelo.com/wp/TestTeam/6/tn_20092440-106938.png
I couldn’t help noticing.
I’m just curious because they have the option to have a better and lighter group set, why not use it?
Personal preference and allot of times when a new model comes out it is not always better than the last. These guys know how to look past the marketing hype.
Part 3 Mark Cavendish Tour de France 2009 EXCLUSIVE
