If it's dropping this year, i doubt it's because they want it to go toe-to-toe with Reach. The franchise doesn't have near the brand recognition of Halo, and I doubt they'd expect a game developed in less than two years to stand up against a game Bungie's been working on since 2007. Not to mention Halo and Killzone are two vastly different flavors of FPS.
If it's dropping this year, they're doing it simply because they feel it's ready. I don't' think it'll hit this year, however. It'll probably be an early 2011 release, though I wouldn't be surprised if it was announced fairly soon (~1 year from release).
They should do a beta over the holidays and include beta keys with GT5. That would help gain the franchise some popularity. :P