I generally don’t comment on this kind of thing, because it’s pointless and a huge waste of time–companies have no reason to pay attention to petitions and the well run ones don’t.
Like the Stop Allowing Returns On E-Books Petition, the Don’t Delete Reviews Petition is not going to have any effect of how Amazon does business, and for the same reason–what the petitioners are asking for would be a bad business decision.
I was working on a way to explain why I think that when I ran across this excellent blog that explains it better than I would have. Go read that.
Adding my own thoughts to Dylan Hearn’s analysis, I would like to remind people that Amazon owns the servers and the software and has no obligation to host anyone else’s words on their site. The reviews that they have on their site are those that they believe will help their customers buy the products that they will be happiest with, because happy customers is what makes money for Amazon.