I must admit that I do get a kick outta how the reviewing gig works.
On one hand (as Tyson points out), a bad review can easily put a dent in a manufacturers sales volume.
On the other hand, a good review, even if sourced from the likes of Stereophile, TAS, etc... , rarely produce the kind of measurable impact one would think they would have.
Most manufacturers know this. Subsequently, you would think there would be little incentive for them to pursue formal reviews. After all, why run the risk? Especially when it's clear that A) there is a good chance that even a glowing review wont bring you a large immediate return on your investment, and B) many of today's audiophiles cast off reviews as "just one man's opinion" at best, and "entertainment fodder/bird cage liner" at worst. Yet after all is said and done, I feel that reviews still have their place and still have their impact.
What it ultimately boils down to is product exposure and credibility. It's funny how so many people will refuse to touch a product that is not well reviewed. These are often from the same people who continually lament about reviews and the reviewers who write them. Yet at the end of the day, most of us are consumers who are all looking for the same thing: a product with a solid reputation for quality and performance. We want to be confident in whatever we invest our money into, and reviews help to establish that confidence. Whether or not an individual review will be responsible for your making the purchase is one thing, but I personally feel that its a lot better to have a few formal reviews to go by than to have nothing at all.