Killzone 2 is heavily hyped because it is an exclusive game for the PS3 that stands no chance of becomming multiplatform ...
Right now the Wii fanboys are in a similar position to what the PS2 fanboys were in the previous generation in that they don't really need to overhype much of anything because (for the most part) sales speak for themself; the Wii is selling well, first party games are selling well, and most third party games of note have sold well.
XBox 360 fanboys are in an different position than most fanboys have ever been because, although the system sales are disapointing, game sales are very impressive and the system has the best library at the moment.
PS3 fanboys are desperate right now because sales of both hardware and software have been disapointing. Any game that is exclusive is now one of the most critical games in their minds, regardless of how likely it is to be critically acclaimed or sell well.