If jQuery is open source, and you look at the source, and you see room for improvement. ... improve it. ... or make a constructive criticism pointing out how it could be improved and someone else will do it.

Could the code be faster? Sure. People often analyze libraries, identify a critical path that is limiting performance, and then zero in on the offending the code ... and then improve it.

I think it's find the author goes on a bit of a rant. Perhaps he'll inspire a few coders (or Resig himself) to address some of the criticisms by revising the code, and then everyone benefits.