I believe this is by design. If you always use the latest beta, you can't load it into an earlier version. This way you can't 'forget'. You do it by choice each time.
If it's a small project, no big deal, but if you're working on the latest mega hit, you might not want to get stuck on a beta with issues (since its a beta) so you would run the stable release to update with. Potentially 'testing' on a beta release if you had a specific issue/function you needed.
That said, I find it a pain too