Gaming PCs are built purely with performance in mind. They all feature dedicated graphics cards, powerful processors and plenty of memory to make sure you get the best out of your games.
PC gamers tend not to replace computers as frequently as normal users. They usually upgrade and add hardware as technology develops to make sure they stay current. Not only is this much more cost-effective over the years, it makes sure you always experience the latest games at their very best.
As you're likely to be keeping hold of a gaming PC for a good few years, it's important to choose one with enough performance to keep you current for as long as possible between upgrades.