This is marketing 101, people. As an author of 9 books, I can tell you that if someone writes a negative review on a book on the day one release (God forbid if that happens before it is even released) it can seriously impact sales for the entire life of the title.
I pissed off a fellow author once and she apparently decided her revenge was to get five fake email accounts and post 1-star negative reviews on my book about 5 seconds after it was available on amazon. If a zero-star review was available I am sure she would have used it. I protested to amazon since it was impossible that the title could have been read in 5 seconds but they refused to take them down. That title tanked, of course.
It only makes sense for Stern or any pinball manufacturer to try to stop people who they feel are not being objective in the reviews of their products.
Actually, what they should be doing, if they are not already, is put their products in front of more people who are objective (or supporters) so that on release you have a bunch of thorough, well-thought-out reviews on the day one product reveal so that the negative-nellies are drowned out.