I've seen so many "collaborative task managers" -- I doubt that the tool is the problem. More the fact that people don't like to do this type of tracking, reporting, etc.
Every project manager (I'm using a very broad definition of project manager here...) wants a system that is almost but not quite what someone has already built. "Ohh this looks nice - wait I can't do X? Then it's totally useless." X is different for everyone. Some people can't live without a versioning system, some pople can't live without tasks that have a sign-off field, etc. There are literally hundreds of ways of doing it.
Nobody has solved this problem yet. Probably because it's extremely hard.
Not all task managers are built the same, but the need a solution is ubiquitous.