On those sites, why cant they give you an estimate of the games they can play, so customers actually get a good idea of what they are buying? Maybe include something like system requierements lab, that tells you an estimate of how well the computer you wanna buy can run the games you want.
Actually, there is a great website that compares laptop video cards and their benchmarks in various games - http://www.notebookcheck.net/Comparison-of-Laptop-Graphics-Cards.130.0.html
It's pretty easy to figure out if any laptop will be able to play whichever game you are interested in.
Basically, if you want to play a recent game high settings at 1600x900 or 1920x1080 resolution, you need a video card at least NVIDIA 460M, AMD 5830M or better (you can refer to sites like notebookcheck to see which cards are ranked better).