Lowercase compresses better?

[rsalz]

In reading
    http://apachetoday.com/news_story.php3?ltsn=2000-09-27-001-01-OP-CY-LF

I came across the following guideline for writing Apache documentation:
    HTML tags should be lowercase wherever possible. In other
    words, '<a href="foo.html">Link</a>' is preferred over
    '<A HREF="foo.html">Link</A>'. This is because lowercase
    letters result in more efficient space savings when documents
    are compressed.

I'm trying to figure out how this could be true.
        /r$