I was advised by the Twisted release manager that the ppa is not as reliable a source for updates as Pypi. He advised doing a pip install --upgrade instead of relying on apt-get-update/upgrade.
That worked and it's fine except that it means we have to remember to do Twisted upgrades in a different manner than many other programs. It's easy to remember (or automate) apt-get. It's another easily forgettable step to have to do the pip upgrade. If we automate the pip upgrade that's adding another level of complexity that I don't think should be necessary.
But most important, I understand that there are only so many hours in a day for people to manage and implement Twisted. If there is going to be a ppa then it needs to be kept up to date. If there isn't time to do the ppa updates then it shouldn't be promoted as a method of updating.