They already do....
Its called ADC Membership.
ADC membership that includes early release software is for development purposes, for people or companies that plan to release software as a part of some kind of business model, generally. Even advanced users, which constitute at least a part of this forum, would be good candidates for helping finding, testing, and reporting bugs in the correct format.
So the average user with little to no knowledge of software. Basically your "internet & email" people would be better at testing software then developers and software testers?
Also to get technical Apple did release the beta of 10. Seeing as how any current revision is going to be an extension of 10. The product (OS X) has been in production for almost a decade, a little bit outside the pre-production that "beta" refers too.
Yeah, I submitted a few bugs for that public beta. The term beta has been bandied around a bit and lost its original meaning; I think Google's one of the worst culprits of this -- Gmail has been in beta since its inception in 2004. The only reason Chrome is technically out of beta, I suspect, is that they need a "production quality" browser if they want any chance of having it ship with OEM systems. But there can also be beta software of new builds, so a beta of 10.6 for instance is not an unreasonable moniker, I don't think. Well, anyway you know what I mean!
By the way, I don't think the Email forwarders and YouTube watchers are the people who would be interested in the testing. But they're also not ones who are downloading and testing nightly builds of Camino or Safari development previews. As a gross overgeneralization, this is probably not the group of people who'd be good at testing, either, and that's fine. They want machines to work and don't care about the process. But there are so many folks willing to help test, it just seems like a great distributed work model.
Perhaps it's the ADC memberships that they feel like they'd be cannibalizing, though those ADC memberships have so much more added value, don't they, like support options and Coding Headstarts, as well as other educational resources.