well, if audio manufacturers only send their equipment to reviewers who have the mentality where they either write a glowing review or send back the product... that means all early reviews from "reviewers" will be universally positive and will not give critical feedback on the product or point out flaws for the consumers.
instead of acting as an unbiased party writing for the consumer market to allow us to make educated decisions, the "reviewer" simply becomes part of the company's promotional PR/advertising/marketing machine.
realistically, it makes good business sense for audio companies to be extremely selective about the people they choose to send out early review units to. They will obviously pick people that they have relationships with or people who have a history of writing really positively about their products. unfortunately, those types of people will write the least helpful reviews for the consumer. In fact, this type of practice will also hurt the audio company since criticism and constructive feedback is the main force for driving innovation and change. (...that along with competition).
of course, individual reviewers have the right not to write or publish negative feedback on a product out of respect for the company. However, it is my strong opinion that sort of behavior not only hurts the consumers, but also hurts the industry as a whole since product flaws are not being identified early & highlighted for everyone's attention.