"And now they have the "most helpful positive and negative reviews" feature, which I think is great..."
Actually they use the terms "favorable" and "critical". You can almost sense the careful parsing that came up with "critical".
"...the helpful votes are not so much about rewarding helpful reviews, but a way to punish people who don't give glowing reviews of products"
Right. People use "unhelpful" to punish reviews that dare to disagree with the majority favorable opinion, regardless of their quality.
Spy magazine used to have the Blurb-o-Mat, an automated praise generator. The Blurb-o-Mat lives on today in the form of a top Amazon reviewer. Everything is excellent!
And as I recall, also something called Logrolling in our Time in which they showed reviews by two authors praising each other's works.
Web 2.0 exploits the worker. Companies take user content for free and co-opt it for the purpose of selling their particular Brighto. Providers of the most free content get the equivalent of a free T-shirt and their picture in the local newspaper. They are chumps.