FYI, bzip2 has been obsoleted by xz which is both faster and gives better compression. But as others have said, Google doesn't care because browsers do gzip.
In the future, browsers could also do xz; they'd just need to advertise it in their Accept-Encoding header. Google could put this in Chrome any time they like, and nothing would break.
As Jach points out above, Mozilla has had a bug[1] open about it for 6 years.