You've never seen an automotive journalist do a review of a prototype? Are you kidding me? They CONSTANTLY do previews of prototype models the manufacturers send them... In fact arguably it makes a lot of the articles you read completely useless as they often get sent cars with specially tweaked engines, suspension, or with all the options.
I find reviews of a beta to be hugely useful if you're making a purchase decision against the product. I think many people read them with the same in mind as per the huge sales of the ePC after it came out of prototype after the publications had been discussing it for like six months before hand.
The only thing better than a review is downloading the beta yourself and giving it a go... Thus the public beta of Windows 7. But for those without the time, expertise(lol), or spare machine to do such testing the reviews offer a good source of information.