Depends on the target-platform for the game. If the game is designed to run on a single platform - say Playstation 3 for example -then it is to the developer's (technical) advantage to develop on that single platform.Interesting - so game developers don't aim for a specific hardware spec max but tweek the end result to fit the current hardware range? I guess it does have quite a bit to do with how rapidly hardware changes and advances in capability during the process of writing the game. Out of curiousity tho are the games generally written on windows boxes or are there propritory OSs for these kind of things?
If the developer can not afford console development kits for each of their staff or if the game is meant to run on multiple platforms then an engine is created (or bought) that allows the game to run on all of those platforms, including PC. The idea behind such an engine is that the game-team should never have to care about the differences between the target-platforms as it is all abstracted away by the engine. It never quite works out that way though, the game-team will always have to manage the differences one way or another.