It looks as if CCC uses a version of rsync which has been patched to support the HFS+ file compression introduced in Snow Leopard. See CCC's
Release History (scroll down to
v. 3.3 (27), September 21, 2009).
A tad more information can be gleaned from
Mac OS X and HFS+ enhancements for rsync 3.
Thanks for ferreting that out.
And I just figured out that my hfs+ compression is intact...that I had run the wrong Terminal command when I originally reported that it had gone south.