The big Money for Sony and MS on Exclusives are not made by the actual games themselves. Exclusives are used to get people to favor your console then buy all the shitty 3rd party games on that particular console.
If someone was debating whether or not to get a 360 or a PS3. Then Killzone 2 comes out and blows them away and convinces them to get a PS3. All the NBA live's, all the spider man web of shadows, all the call of duties, the guitar hero's, the far crys the Maddens that that user buys can be chalked up as revenue generated by Killzone 2, generated by Heavenly Sword, generated by MGS4, generated by whatever exclusives helped get that consumer to buy a PS3 over a 360.
That is why games like MLB the Show, Eye of Judgment, and Buzz! which may not sell a ton are important. Because there are baseball fans out there or niche genre fans out there that will buy a PS3 just for those games. Then all the additional games that they buy on the PS3 is revenue generated by those niche games that may not sell a lot of copies themselves.
It remains to be seen if Killzone can push consoles. But it definitely will add to the pot of PS3 exclusives that will help lure potential HD console owners over to the dark side. And it will definitely be a worthwhile investment on Sony's part.