Let's see what happens to sales in the lead-up and weeks/months following GT5's release.
Who knows whether the study was conducted properly, but the findings don't seem off: if 10 million are going to buy GT5, 3.9 million haven't even bought a PS3 yet, though it's 6 months till the game comes out.
You think Halo 3 moved 4 million 360's? I'd say more.