The Problem With Porting Games on bit-tech.net talks with developers about the art of porting games from one platform to another. CPU and GPU architectures are analyzed, graphics, testing, and more. It's an enlightening read, as demonstrated by this discussion of PC ports:

The problem for multi-platform game developers making PC games is that at some point you have to say “stop” when it comes to extra hardware features. You can always add higher-resolution options in the PC game, but you begin to upset the guys in control of the game's budget if you start putting serious man hours into developing graphics features that are only available to a small number of PC gamers, let alone console gamers. “I know people are going to read this and say, god that guy's telling us that we've bought all this hardware for nothing,” says Bozz, “but the reality is that as much as I'd like to support this stuff, I can't do that at the expense of the other 98 per cent of gamers.”

A very common bugbear for PC gamers is that they feel that the graphics in a PC version of a game have been compromised, simply because the consoles wouldn't be able to handle the same level of graphics. However, Red Faction: Guerilla's system architect Dave Baranec disputes this, and says that in fact “we usually find it's the opposite”.

Part of the problem is that multi-platform games are usually developed primarily for consoles, which means that they're heavily optimised for those architectures. Baranec explains that “content targets, system design and overall structure tend to be tailored towards what the consoles do best. It isn't uncommon to find that even high-end PCs have a hard time holding up against the sorts of deep optimisations you can make on fixed hardware.” However, he also concedes that “the situation could certainly be reversed – you could build a game that caters to the strengths of PCs, and find huge problems trying to get it to run on a console”.