Keep in mind that when you label a version "beta", you get less people using THAT version compared to a version labeled "stable", which in turn means far less chance of bugs being caught in that period.
Yes, but if it is publically available AND had a forum for discussion, that would increase it a LOT! The way it is now, everyone has to individually report errors, and they can't see what other people have reported, and it gets old reporting every tiny bug because you know that other people have obviously seen them... but no way to confirm that.
Also, people keep reporting the same "stable" bugs over and over because they have no way of knowing that some of those issues are already fixed in the next beta version... because there is often no changelog at all for beta versions and no where to discuss them. If there was a place to discuss beta versions, you could see that "xx" issue is either fixed (and that "xx" bug tested specifically be users) or not yet fixed in the upcoming release.
Like this current Winbox bug in v6.4 for instance, it MIGHT actually already be fixed in the 6.5 beta... but if I tested 6.5 beta for that bug, I would not be allowed to tell you here on the forum if it is fixed or not! So, EVERYONE that has development access would have to test it themselves instead of being able to see that a few people have already confirmed it one way or another, if they wanted to know if it is fixed.... instead of spending time looking for other bugs, all beta testers are spending time testing this one obvious bug.