Bugs aren't closed unless either a developer fixes the report, or they are re-tested at a later date and found to be working now. Us developers go through the full list regularly (including the oldest ones) and review all of them, and a bug won't be closed unless it can be proven fixed. I won't close an old bug just because it's old, it still needs to be fixed. Also, I'm sure nearly all of them are bugs, since feature requests should not be on the bug tracker and I immediately close any reports which are not bugs (and I don't think I've seen many on there).
I don't think it's a mess. It's a relevant list of all the problems currently in Construct. It's miles better than having reports strewn around a forum being forgotten about.