With the move to 3.x Linux kernels, Debian introduced new meta-packages
for them:
 * linux-image-amd64
 * linux-image-686
 * etc, basically just droping the "2.6" from the name
The old 2.6 packages still exist in the archive as of today, but I bet
they will be droped at some point in the future.
Especially they are already droped from the ISOs for the upcoming
release (Wheezy).

Because of this, kernel() from chroot-script will fail to install a
proper kernel when executed in a >= wheezy chroot with only the ISO
available as a source for packages.