Where has Sony ever said Killzone is intended to rival Halo?. To get 10million+ sales takes more than a quality game, marketing, it needs to seep into mainstream culture and become an iconic game. A good example is Microsoft putting huge resources into the Forza franchise so it rivals Gran Turismo. What have they got to show for it?. Zilch is the answer. How many franchises in the industry are capable of these type of sales?. Halo, Gran Turimo, GTA and now Call of Duty is all.
Also costs to develop Killzone 2 was pretty much on par with other bigger titles from Sony at 27 million Euros.
Name a market where competitors don't naturally create rival products? You think Verizon and T-Mobile are going around calling their Andriod based phones, the "Iphone killer"?
Were you not around in 2005? How many Sony published PS3 titles got as much exposure as KZ2 from Sony over the years. The only ones I can think of is GT and LBP. KZ2 was shown by Sony in 3 out 4 E3 before release. In contrast, UC never received anywhere near that kind of push. TV and print commericals aren't the primary marketing tools for games, its widely followed events like E3 and sites like Gamespot that generate the most hype and the most efficient way to market to core gamers. Heavy TV and commerical marketing blitz are very expensive and are only used by titles that have already reached blockbuster status. Halo1 and Gears were able to achieve 5 million+ in sales with way less exposure and smaller userbases.
You don't need to do 8 million in sales to rival Halo on the PS3 platform, you just need a iconic exclusive FPS title that can rival for the top podium of the PS3 library based on sales and critical acclaim, which from all the evidence out there is what Sony was attempting with KZ2. How many companies have pump 27 Euros (whats that like 40 million dollars?) into a title with the intent of something other than blockbuster status.