I'm pretty confident it's because Cervelo's are built like Treks. I dont know what kind of bike merckx rode, (probably not a merckx bike itself). I know on my Trek it's much harder to reach the drops, and that's why CSC guy is in the hoods, the drops are more uncomfortable.

Also notice the position of the hoods on both bikes. The ones for the CSC rider are much more accessible. Merckx actually has to reach around the handlebar to get them - meaning he will likely spend more time in the drops.