[CentOS] Let's talk about compression rates

http://pastebin.com/raw.php?i=MwDnhknf

$ ls -Sl total 461252 -rw-rw-r--. 1 g g 111709730 Jan 22 11:06 linux-2.6.37.zip -rw-rw-r--. 1 g g 93174605 Jan 22 11:03 linux-2.6.37.tar.gz -rw-rw-r--. 1 g g 73552510 Jan 22 11:10 linux-2.6.37.tar.bz2 -rw-rw-r--. 1 g g 66333786 Jan 22 11:16 linux-2.6.37.7z -rw-rw-r--. 1 g g 64035788 Jan 22 11:16 linux-2.6.37.tar.7z -rw-rw-r--. 1 g g 63480808 Jan 22 11:20 linux-2.6.37.tar.xz $

I presume kernel.org knows this. Why doesn't people use e.g.: XZ?

This is the same as in PDF's. DJVU files could be amazing too. They could compress [convert] a 400 MByte PDF to a 20 MByte DJVU. Amazing.

Why don't these technologies spread??

Any opinions regarding it?

Thanks.