The first thing that comes to mind when you see results like this is a cry of foul play; that Valve has unfairly optimized their game for ATI's hardware and thus, it does not perform well on NVIDIA's hardware. Although it is the simplest accusation, it is actually one of the less frequent that we've seen thrown around.During Gabe Newell's presentation, he insisted that they [Valve] have not optimized or doctored the engine to produce these results. It also doesn't make much sense for Valve to develop an ATI-specific game simply because the majority of the market out there does have NVIDIA based graphics cards, and it is in their best interest to make the game run as well as possible on NVIDIA GPUs.Gabe mentioned that the developers spent 5x as much time optimizing the special NV3x code path (mixed mode) as they did optimizing the generic DX9 path (what ATI's DX9 cards use). Thus, it is clear that a good attempt was made to get the game to run as well as possible on NVIDIA hardware.To those that fault Valve for spending so much time and effort trying to optimize for the NV3x family, remember that they are in the business to sell games and with the market the way it is, purposefully crippling one graphics manufacturer in favor of another would not make much business sense.Truthfully, we believe that Valve made an honest attempt to get the game running as well as possible on NV3x hardware but simply ran into other unavoidable issues (which we will get to shortly). You can attempt to attack the competence of Valve's developers; however, we are not qualified to do so. Yet, any of those who have developed something similar in complexity to Half-Life 2's source engine may feel free to do so.According to Gabe, these performance results were the reason that Valve aligned themselves more closely with ATI. As you probably know, Valve has a fairly large OEM deal with ATI that will bring Half-Life 2 as a bundled item with ATI graphics cards in the future. We'll be able to tell you more about the cards with which it will be bundled soon enough (has it been 6 months already?).With these sorts of deals, there's always money (e.g. marketing dollars) involved, and we're not debating the existence of that in this deal, but as far as Valve's official line is concerned, the deal came after the performance discovery.
Once again, we're not questioning Valve in this sense and honestly don't see much reason to, as it wouldn't make any business sense for them to cripple Half-Life 2 on NVIDIA cards. As always, we encourage you to draw your own conclusions based on the data we've provided.