More than likely the ultimate culprit. It's not really fancy in the graphics department so they probably made it piss poor in the optimization department and called it a day to save some debugging money.
Are you checking the clocks? The gpu might be running at like 500mhz which would result in a 90% load even though the video card isn't really using its full power. I've seen that happen in games that are really easy to run. --- Currently Playing: Kid Icarus: Uprising, Donkey Kong 64 and Fez