The approach is not perfect. If the central copies are corrupted or infected with malware, every website using them could be jeopardized. But when was the last time this happened? Switching to a local version of the libraries, the simplest fix, wouldn't be hard.
Browser as ultimate OS reason No. 8: Fertile, competitive marketplace
Once upon a time, there was only Netscape. Then Internet Explorer dominated. Now it seems like everyone has a browser that's competing. Chrome, Firefox, IE, Safari, and Opera are just the beginning. There are dozens of other minor browsers with their own devotees. The mobile platform has even more.
All of them are competing for eye share. The best one wins, but only until the next upgrade cycle. Then the competition begins again.
This battle breeds quality. The best browsers with the most useful features flourish while the casual hacks disappear. This doesn't always happen in the world, but when it does it's great for consumers. When it's good for consumers, it demonstrates the power of the browser layer.
Browser as ultimate OS reason No. 9: SVG, canvas, vector graphics, great user interfaces
The early Web pages may have been slightly dull, but that was before clever programmers figured out how to animate the CSS properties of a DIV or a SPAN. Now rectangles and the words within can flip, spin, turn, fade, blink, and even -- perish the thought -- just sit there.
Browser as ultimate OS reason No. 10: Node.js
The package offers spectacular performance for some jobs simply by tossing aside the threaded model common in past generations. Instead it adopts the callback function, one of the idioms of browser programming, to juggle the workload. In the right hands, programmers can sidestep the dangers and produce a clean mechanism that dishes up the information from the server quickly and efficiently.