Codemasters Community Manager, Ian Webster, had this to say on the matter:
"Due to the nature of the game, and its layers of licensed content, it will not be possible to make a cut-down, limited content sample that would serve as a demo for F1 in 2010 within our production deadlines."
I don't know exactly what this means but it would seem quite simple to me to make a demo for a racing game. Just include 1 track and 1 or 2 vehicles to choose from and voila. Anyways if you aren't sure about the game simply wait untill a few days after release to get an image of what it's like through some reviews.
