In the development of a AAA game title, the game studio will often get help from PC component and console makers to help them ensure the game title in question will function correctly on the hardware in question. For example, nVIDIA and AMD will send GPUs to the development studio for testing purposes and might actually give money to the studio to offset the cost of developing optimizations for each GPU etc. nVIDIA’s The Way it’s Meant to Be Played is a perfect example of the effort these companies go to ensure proper performance. This same situation exists at the console level. Sony and Microsoft give not only existing hardware, but also information about next generation hardware to game developers to ensure proper optimizations for new game titles. Groups like Activision Blizzard get this level of involvement and support.
In a world where Activision Blizzard is owned by Microsoft, Sony would be giving details of their next generation consoles to Microsoft. It is either than or face unoptimized games, delays in releases etc. All these things will directly affect Sony and their sales, even with a licensing deal from Microsoft. The reality is that the size and scope of Activision Blizzard will have such a negative impact on the console gaming market that is does not make sense to allow Microsoft to buy them. Of course, I would argue that allowing any Console company to directly own a game development studio is a bad thing which impacts the environment in a negative way. Granted mergers and acquisitions happen all the time and nothing is ever going to stop that. This does not mean that we should not take a long hard look at deals like the Microsoft Activision one and stop them before they create the massively negative market that it clearly will.