I was thinking pedantically that there are more powerful "computers" available than a high-end PC and they would be able to do even better than this example, but then it occurred me that it's also possible that game engines are the most sophisticated physics/graphics engines... worldwide, they probably have more attention and money focussed on them than even the US military could afford (guessing).
http://www.gamespot.com/pages/forums/show_msgs.php?topic_id=... for an actual gamers review w GTX 260.
However, the average frame rate is almost useless, it's the minimum that's important and an absolute minimum of 24FPS on the most demanding demo is perfectly playable. Mostly when you play the game it's far higher than that, but in the middle of a huge firefight when vegetation is being chopped to bit's it's still playable.
PS: I wish most reviewers would note the worst frame rate instead of letting 100FPS in some areas cover for sub 30FPS in others. EX: http://www.guru3d.com/article/palit-geforce-gtx-260-sp216-so...
Why do our expectations drop so drastically just because something is downloaded from the web and run in a browser? Not that there's anything wrong with that, but accessing something via web and running things naively aren't necessarily mutually exclusive.