I'm not sure how much the rate of audio/video equipment failure has to do with whether or not to purchase from unauthorized dealers. If you do any kind of research on the internet (sites like resellerratings.com), you will see that many of the problems associated with unauthorized dealers are not related to the longevity of genuine name brand products. Most have to do with folks not getting what they ordered. In far too many cases, they get gear in boxes that are obviously not factory-sealed, used gear, damaged gear, refurbished gear, gear that is dead-on-arrival, gear with serial numbers removed/obliterated and, I suspect, in some cases, counterfeit gear.
Another common complaint is that of unauthorized dealers just outright lying to customers. All too often they will tell you that the product you want is in stock when it is not. You only find out the truth after your credit card has been charged. Then you are faced with either waiting or canceling your order. Other problems are ignored e-mails, unanswered phone calls, etc.
If one could be assured that when they ordered a receiver from XYZ E-Tailer that they would get a brand new, factory-sealed unit, sent to them in a timely manner, perhaps there might be a reason to go ahead and get it at a greatly reduced price. But, unfortunately, there are no such assurances -- at least which can be relied on. Sure, the E-Tailer will make such assurances, but I wouldn't trust the "typical" unauthorized E-Tailer any further than I could throw him.