If it was beta software that only a few people are never likely to use them it should be closed as it would not have a widely applicable audience. Bugs in beta software are subject to flux and get fixed quickly and so a question about specific bugs would have only a small time window of applicability.
The Windows prerelease software is, essentially, available to everyone and a lot of the questions asked will be applicable moving forward into the RTM release and so would be useful to have from this point onwards.
Both those points being important I would suggest that we need to split Windows 10 questions into two categories.
- Beta program type software bugs
- questions about using the operating system
Beta bugs should be closed in my opinion and the user pointed at the Microsoft site in order to report them. Asking them here is not constructive. Microsoft want to know about the showstoppers and broken features before release but we do not as a site as they are fleeting. (not that we aren't curious though)
If on the other hand it is an obvious feature that will certainly make its way to RTM then I am fine with it being asked here.
Granted it can be difficult to tell the difference but if you see a question that essentially says
I pressed button X and the whole operating system formatted itself. Its not meant to do that, stupid buggy Micro$oft rubbish. Lol.
Along with several users saying "yeah, that's a reported bug, its going to be fixed" then that question can die in a glorious burning fire as far as I'm concerned.
I'm sure we used to have a "beta software" close reason, I'd consider seeing that set back up to close the more useless group of questions.