[bmelton]

jQuery is, not so arguably, the most popular general Javascript prototyping framework.

A 'regular' Javascript library would likely not get as much attention as its jQuery equivalent due to all the momentum behind jQuery itself.

[richbradshaw]

I think this comes from the idea that it will be easier to integrate/extend understand, as much of the complex functionality moves out of the project and into jQuery. That means that often the project becomes smaller and easier to digest.