Comment 2 for bug 16759

Oh, yes. Of course. It's been so long since I switched that I forgot
completion wasn't enabled by default without a compinit call.

Would you consider accepting something like the following:

# If you don't want compinit called here, place the line
# ubuntu_skip_compinit=1
# in your .zshenv
if [[ "$ubuntu_skip_compinit" = "" ]]; then
  autoload -U compinit
  compinit
fi