I think they are referring to Diesel engines since in that paragraph they talk about knocking and Diesels.
From this link:
http://www.caranddriver.com/features/04q2/will_gasoline_direct_injection_finally_make_it_-column
"The direct-injection system then takes this hardware up a notch. First, the evaporation of the tiny droplets of fuel injected directly into the cylinder (at between 450 and 1700 psi) cools the intake mixture, producing a denser charge, which means more power.
Furthermore, the cooler charge is less prone to detonation. Further detonation resistance comes from more rapid combustion, which occurs because although the overall charge mixture is stoichiometric, the charge is locally richer in the vicinity of the spark plug. This causes the mixture to light off more vigorously and progress more quickly. Faster combustion means less spark advance, which is inherently more efficient and further reduces detonation sensitivity."
Not sure which is right but it's an interesting discussion. Too bad I play with servers day in and day out rather than cars!
True - I'll stick with what the book says and hope it all works out.