History of the browser user-agent string
webaim.org
webaim.org
Of course, your browser could lie about its capabilities, as many Direct3D drivers do. And you will still need to test in every single browser, as game developers need to hire labs to test on the 150 most popular 3D cards.
Although, a web browser IS web-connected :-) We could have another new string which is "I swear I am actually this browser and version." and someone (cough Google? cough) could create a web service with a mapping of real browser agent string to real tested no-foolies caps.
game developers need to hire labs to test on the 150 most popular 3D cards
With this in mind, I find it odd that console games cost exactly the same as the PC version. Surely they can pass some of that savings (from only having to test on one machine) on to me? :P