Re: The problem is browser offer an execution environment, but not "system" libraries.
"Since browsers are nowadays updated frequently, the user gets the latest version of library, and no wasted bandwidth"
I refer the honourable gentleman to the post I read some moments ago. If we could rely on everyone to be running a recent browser, a fair number of common JS libraries could be dispensed with altogether. Trouble is, we can't depend on that, or at least we believe that we can't.