DannoXYZ 

Good eye Snuffleupagus, the extended leg does look a little too bent. Photos of the pros below show that leg being almost fully extended.

The thing is, habits are hard to break and it's best to be flexible (literally and figuratively). The position looks an awful lot like Sean Kelly's and who knows how great he could've been if he wasn't locked into his cramped position based upon riding a childhood bike.

Being aero, being able to operate at high-levels, and being comfortable for hours on end in races is a tough combination. In terms of speed, getting more aero is always a tonne easier than increasing power-output by a comparable amount. The top riders will typically show a stretched out position that allows them to get their heads really low (notice forearms going forward at 45-degree angle):






Having forearms that are close to horizontal also has the added benefit of having only as much drag as your hands:






And being aero (notice side-stripe of jerseys are parallel with ground & top-tube) not only makes you faster, but also makes the guys behind you work harder.