That might be the case. This blog post [1] shows some examples of what the advance optimizations do and it seems that, while it'll shorten everithing up, things that are put in the global namespace (window) will not be stripped even when they aren't called. As jQuery adds the 'jQuery' and '$' variable to the global namespace and all it's functions are attached to that object, I would assume that the Closure compile connot remove any of them.

Of course, this is all pure speculation, it'd be much better to test this out.

[1]: http://www.bitstorm.org/weblog/2010-8/Introduction_to_the_Go...