In the majority of cases, I think both of these are true. Occasionally we do get some topics that can be merged/re-opened, but more often than not a separate topic per issue is the right way to go.
The auto-bump feature we use on meta is a little controversial. It has at times been called an anti-feature and some community regulars have regularly expressed their strong feelings of annoyance with it… The main reason it was started in the first place is to tidy up older topics (the older the better), and update, close off, mark solved, recategorise, or delete them depending what pops up. I think it’s been acknowledged a few times by various people that it’s more useful for those organising the forum rather than those browsing or contributing.
So far, I have left the tradition in place, mainly because I haven’t yet got a replacement for it and having 3 or so topics bumped a day seems manageable and not too noisy (though I appreciate it’s a trade-off).