I think picking jQuery as an example wasn't the best choice since it probably is already cached for sites that use google's or other popular CDNs. This is true for StackOverflow (one of the examples in the article).

The main point of the article still stands though. Closure and similar tools make a lot of sense because they can reduce the size of js quite a bit. Especially for huge apps that require several libraries but only use parts of them it can make a huge difference.