I agree, my current computer is three-to-four years old and I still use it on a daily basis. I've been through three phones in that amount of time. According to that logic I prefer my phone 3-to-1 over my computer yet if I had to choose I would drop the phone over the computer without thinking twice.
Plus, do the numbers account for saturation of the marketplace? PCs have been around for quite a while, Android and iOS have a much shorter lifespan with sales that have not peaked. I ask because I didn't read the article fully since I tend to avoid pronouncements such as "this thing here is dead!" we get every couple of months. Talk to me when PC sales have been trending seriously downward for five-to-ten years and then we can discuss the death of the platform.