I've always used the ppa
I'm sure many people do, that's not the point. Ubuntu is one of the largest GNU/Linux distros around, and their average user had access to bitcoin as part of their operating system. It would be as if windows 7 had came with an option to install bitcoin via an optional windows update or something. Today is release day for 14.04, perhaps it's worth reflecting on what we just lost.
Exactly, why would they include Bitcoin? I wouldn't expect anyone to. Not some anonymous os maintainer. I'd rather get it from the ppa and know the guy doing it. You must trust their signing keys.
If you do not trust the Ubuntu repository and their maintainers, you shouldn't run a bitcoin client (or anything else sensitive) in Ubuntu regardless of where you get it from, that's a really stupid argument.
Since you already have to trust Ubuntu, trusting additional sources (and you would have to do that for more than just bitcoin) raises the bar considerably, and does not improve your real security.