The Microsoft Genuine Advantage, is just that. Its an advantage. In over 15 years of my profession not even once has Microsft denied me or my customer support for a genuine product for any reason. In fact I remember clearly an incident where my clients install disks were damaged for WFW 3.11. This was before the modern advances in software validation. The hard disks had failed and we had to start over. This was back before the OS shipped on CDROM. Microsoft Overnighted 13 floppies to us and we did not have our Product ID, or Install Keys. All we had was the purchase reciept from the hardware vendor. Oh and I forgot, they paid for the shipping!
Another (more recently) time a windows 2003 server was down at a municiple building. I was not the contracted vendor. I just happened to be the guy they called. It was Friday on a soon to be holiday weekend. They answered the phone and based on our Product ID on the Server OS, we were escalated to the proper department. Then after a little research the engineer was able to pull up our support options which were outstanding. In less then four hours we had an Engineer assisting us with the down server. If not for excellent registration and software authentication systems this kind of service would have not been possible.
Product Authentication & Registration is absolutely the same as registering your car for the manufacturers warranty. The auto manufacturer would not warrant a car they could not verify was from their factory no more than a software company will warrant or support software that it cannot authenticate.