There are many businesses and companies out there that are in competition with each other. However these companies end up creating such different products for different purposes that their competition is less and overtime. I think that is what happened here with Microsoft and apple. People either bought apple products or they bought Microsoft products depending on the type of computer that they were using.
Sometimes a company like Microsoft will focus so strongly on one type of product that their competition is able to surpass them because they are trying to find a variety of products to sell two all consumers. These consumers were probably wants Microsoft consumers and then turn to apple based on the variety of products that were sold by apple.