For Google products, huge gains come from running an optimizing compilation (Closure Compiler) which dramatically rearranges Javascript the same way GCC rearranges C into assembly.

It is not always true that minifying method names is the same as gzip, as a good minifier will understand scopes and arrange many of the variables to have both the same name and smaller distances between like symbols. This shifts the frequency distribution of the symbols as well as the distances allowing the huffman coding to be more optimal.