The Sound of Silence
Take a look at this chart from BoardReader which tracks forum postings about Borderlands and Killzone 2. Both games fall into the same genre (sci-fi FPS) and will be released roughly around the same time. Even though people are saying that Borderlands will be a better game and Killzone 2 is only on the PS3, there's a ton more talk about Killzone 2.

What gives? Read on after the jump for our 2 cents.
Borderlands is the first in a franchise. Killzone 2 already has a giant advertisement in the original Killzone to promote it. Borderlands doesn't have much to generate interest other than some preview videos, screenshots, and, of course, the always insightful observations of BorderlandsGuide.com.
That red squiggly line riding the bottom of the above chart will eventually jump. But first, one thing’s got to happen. Gearbox must start talking about the game.
So far, they’ve been pretty mum. We understand, they’ve been busy releasing a couple other games. Now that they’ve got Brothers In Arms: Hell’s Highway and the history’s greatest samba sim on shelves, their marketing attention can shift.
We suggest a major advertising campaign featuring the girls from the Samba De Amigo commercials. Dancing women in bikinis are always an excellent way to increase brand awareness. Don't you agree?

Agreed.
"It is by the goodness of God that in our country we have those three unspeakably precious things: freedom of speech, freedom of conscience, and the prudence never to practice either of them. " - Mark Twain