> I bet if you sorted all the ".deb" packages on a mirror by size a lot of them would have a similar or the same size

Why bet when you can science? :)

  $ rsync -r rsync://ftp.be.debian.org/debian/pool/main/ | grep "\.deb$"
  $ wc -l debian.txt
  1246733 # total number of deb packages
  $ cat /tmp/debian.txt | awk '{ print $2 }' | sort | uniq -c | sort -rn | head -1
   463 1044 # The most common package size has 463 occurances
  $ cat /tmp/debian.txt | awk '{ print $2 }' | sort | uniq -c | sort -rn | awk '{ print $1}' | grep -c "^1$"
  259300 # The number of packages with a unique size
  $