While Ubuntu takes most of its packages from Debian, it does contain a few that are not in Debian, for one reason or another. One common reason is simply that someone wanted a package that wasn't in Debian, and packaged it and requested its inclusion.
Read it here
The packages that we have in Ubuntu universe but not Debian don't have too many bugs, but the ones that they do have are under-triaged, and we aren't that aware of what bugs we have.
Also, we could do more to allow our automated tools for finding out about new upstream releases work better, again making sure we are aware when a package is out of date