Marc, I disagree. Solving every issue and whim that every user files against a popular package, while not letting the package degenerate into a mess, is hard. Taking some time to gather opinions and produce a well-designed fix that strikes to the core of an issue, rather than treating symptoms, is a good thing for many classes of bugs. (Other classes should instead be fixed immediately.)
The existence of many open bugs against a package in Debian is not an indication that it's of lower quality than the corresponding package in Ubuntu -- which in fact probably has 99% of the same bugs anyway.
As a user, I also regard a BTS as perhaps the best form of documentation there is about real-life problems that I might encounter while using the package, the general quality of the code in the package, etc. It's the first thing I look at when installing some new peice of software. It's also a good way to gauge how well the package is maintained -- not by counting bugs, but by reading how the maintainer responds to bugs.
What I look for in a BTS is an indication that the maintainers care about a bug. The fact that Debian bug #725 took ten years to get fixed doesn't mean that X's maintainers suck, it means that for ten years, we were able to document a minor problem to the few users who cared about it, and that we were able to keep track of it until someone finally figured out how to fix it. That's quite an accomplishment.
Another example, to keep picking on X, the fact that Debian bug #216933 is marked wontfix is not an indication that the bug is worthless; in fact the bug documents a quite subtle issue in the Crusoe's code morphing software, and has been an invaluable reference to a lot of Crusoe users.
I'm much more concerned about all our users who don't know about the BTS and are unwilling to bother to file bugs than I am about the total number of unfixed bugs in the BTS. Getting 100% of our users to file good bugs on every issue they run into would do much more to increase the overall quality of Debian than fixing every > 1 year old bug in the BTS would.