Yup, I agree with you (about the whining that will happen).
However, the way the linked article reads above is that MS wants us to wipe and install Vista even before a clean install:
"We want to encourage you to revert to a Vista image and upgrade or to do a clean install, rather than upgrade the existing beta," Microsoft said in the blog.
I guess that doesn't say it's required, but I just want someone to say expressly that if I'm wiping a partition for this, I shouldn't have to install another OS before I do that.