I'm the OP in question. I did manage to run Update Manager for part of
the updates, so I now know which ones wanted the DVD.

Those were:

build-essential
DKMS
libalgorithm-diff-perl (new install)
libalgorithm-merge-perl (new install)

I am not planning on reinstalling, as I want to remain at 10.04 LTS
until 11.04 has been out for a while. And I have no plans to install
10.10, which is the DVD that is being requested.