Perhaps, but it does seem that the Google Closure developers are unaware of these optimizations. Unless the compiler was written by an entirely different group, I would be surprised.
Closure was written by many, many different people. I can attest that the core developers (the ones whose names are on the project) are very aware of these optimizations - one of them interviewed me when I was being hired, and another was in charge of my JS readability review. But Closure's a big chunk of code, though, and the core developers tend to be very busy people, and not everyone can review everything.
Of course, there's an easy way to find out. :)