Trying to understand the package pools

[bryan@bryansweb.com]

Quick question . . .
	Maybe I don't understand the package pools yet but I noticed today
that when searching for for the package kernel-source-2.2.18 on www.debian.org,
the only thing that the site returns (for either stable, testing, or
unstable) is the pre-release package:

kernel-source-2.2.18pre21_2.2.18pre21-1_all.deb

The link to download the package shows it sitting in the 
dists/potato/main/binary-all/devel/ subdirectory.  However, when
digging around the ftp site, I find this package:

kernel-source-2.2.18_2.2.18-1_all.deb in a separte directory:

pool/main/k/kernel-source-2.2.18 subdirectory.  Is this a problem with the
package pools?  Or is there a reason the Debian web site doesn't link to
this second package?

Thanks!
Bryan