I think Microsoft did make the RC available publicly, but the "free copy" was available to techincal beta testers who met Microsoft's crteria for "active beta testers" (though they never specified what that meant). The free copy was in the form of a download and license key, or installation media (shipped later) - but not both. Once you opted for one you could not change your mind.
To my knowledge there was never a "technical beta" for Windows 8. Having been through several of them in the past, though, I can imagine why:
FAQ #1 in the newsgroups: "when will we get another build to test?" (sometimes MS offered "interim builds" between milestones - they were usually "buggy" so when an interim build proved less than ideal the next question was essentially "can we have another one that's better?")
FAQ #2: "Will we get a free copy?"
I imagine that because of that sort of thing and the constant leaks, MS probably discontinued technical beta testing.