This is nothing against uglify. Rather, here's the story on this:
Commit e4cd1e fixed an error that was causing minified files to break in IE.
This was due to how IE interprets things, not how UglifyJS was minifying them.
Indeed, Closure Compiler had the exact same problem.
The decision to move to Closure Compiler was due to a variety of factors, which
came down to primarily feature set and tests. Closure Compiler is well tested
and maintained. It also includes a number of additional, beneficial features.
UglifyJS is an excellent project and I would recommend it to anyone, but it is
not tested (no unit tests; it's tested by ensuring common libraries like jQuery
run after minification). It is, however, significantly faster.
It's likely that, in the future, once I add autoconf for the build process to
configure certain settings, that I will add UglifyJS as an option. I'm sure many
people would prefer that, especially those who dislike Java and do not wish to
have it installed. Hopefully those that do decide to install Java will go with
openjdk, not Oracle's proprietary implementation.
Mike Gerwitz