PC games these days are largely restricted to the console architecture available at the time. The vast majority of them are simply ports of the console version, so while PC hardware might advance in leaps and bounds, the requirements for games will remain the same until the next generation of consoles. And while there are a number of PC only titles, they generally follow the requirements of the console ports in order to stay relevant to the general gamer user.
See above. The console architecture coming out soon is not very demanding. You can already get PC hardware that exceeds the requirements, and that gap will continue to grow until the next generation of consoles comes out. Both Microsoft and Sony aim for a 10 year product cycle, so you can build a system now that will be more than sufficient for the vast majority of games that will be released during that time. And once you have your basic setup, provided your using PC and not a Mac, it's not that difficult to upgrade individual components as you can afford them.