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.
Because Bitcoin is supposed to be a universal/global payment system. I would expect every serious operating system to support it out of the box, at least to some extent(using the QT client specifically isn't strictly necessary, but at least something for their users to interact with the world financially should be a pretty big must have). It's like having a computer without a web browser...who would even do that? This is 2014, not 1985.
How does Ubuntu manage to keep all their other software secure? We don't seem to have problems with their bundling of Firefox, or GCC (
http://cm.bell-labs.com/who/ken/trust.html ) or even some of the libraries that Bitcoin uses (libc6). Why should Bitcoin-QT be any different?