I'd have said yes to the 6 years guess a month ago but.... I'll get back to that.
now granted, graphics cards are a lot better at rendering... graphics than a CPU is but it'd take my fairly meaty PC about ten minutes to render one of those images of Chief's helmet (either the supercloseup visor one or the one that pans back about a foot or so) and my computer is no slouch, not bleeding edge any more but not slouch.
That said, there are ways to cheat, if you've seen the Lost Coast expansion for HL2 then you'll have seen the displacement maps in action, they're used to add a fake bit of 3D to a 2D image with considerably less processing overhead than actually rendering a 3D model of that level of complexity.
Heh, I had two paragraphs trying to explain this if you weren't aware of the concept but http://www.spot3d.com/vray/help/VRayHelp150beta/examples_displacement.htm
does it much better. The first comparison is what we're talking about, both images are of a regular sphere, post rendering. The bump map *looks* bumpy but if you look at the edges it is shown up as an illusion. It is commonly used for skin rendering since pores and wrinkes don't look so obvious when they smooth out at the edges of a face. Bump maps take the sphere and extrude shadow maps *outwards*.
Displacement maps on the other hand move inwards - in that example, the most extruded bump actually only reaches the outside of the sphere's geometry and the model is rendered by cutting out all the bits the renderer thinks you won't see.
Take a look at Unreal Tournament 200...7? I think. It has a similarly high level of detail to all the models as Halo3 but with a more cartoonish shader applied to it, possibly to obscure some flaws, I don't know. It also bears mentioning that your hardware, my hardware and hardware in general are limited by the capabilities of DirectX. When version 10 comes out you're going to see some MASSIVE leaps in performance from your computer without any changes on your part... assuming you upgrade to the new version of Windows too. By that same token, every new version of the drivers increases the performance by leaps and bounds. So, given that it is developed exclusively for XBox 360, which is powered by the best Microsoft can provide and its hardware is geared exclusively for games... well it isn't THAT much of a leap to believe it might be capable of those kinds of images.
Hell, I thought oblivion was going to kill my machine but it runs quite happily on high settings and looks amazing.