Upstart jobs are stored in /etc/init/. There is lots of them on a lucid lynx system :
$ ls /etc/init | wc -l
But that's mostly replacement for the old /etc/rcS.d/ system.
I guess there is more of them on a up to date ubuntu ( for example, I found cobbler in precise, and I guess there is ).
In fact, the real issues is not "using upstart vs using systemd".
The real issue is :
- switching to systemd
- keeping upstart
Switching to systemd is not just a upgrade when coming from upstart, since you cannot just replace upstart jobs by systemd jobs. So I can see why the Ubuntu team thought it would not be worth. They seems to have suffered from switching ( http://undacuvabrutha.wordpress.com/2011/04/29/why-ubuntu... ). So I can see why they prefer to focus their resources to more differentiating features than a init system.
That's transparent to users, and while I definitely prefer systemd ( cause this is much easier for packagers and sysadmins, and much cleaner with the template system for stuff like openvpn ), if desktop users are not gonna see much, this is maybe not the right time to do a big change again.
I do not think this will be a huge burden on Canonical since Google also use it and they have enough people to take care of that.