1) Microsoft wants to create a coherent store experience and ecosystem for Windows with the Windows Store.
Let’s be honest here, when Apple showed the world how awesome a central managed application store is, everyone had to do it. Like the mouse, touchscreen and GUI interface, it’s something that can’t really be considered as a stolen idea or copying the other since it’s just an obvious thing that nobody got before. The Windows Store is here to stay and the design of those apps are to be structured for a coherent and unified experience. It doesn’t make sense anymore to scout the web through bad website and installers that want to fill your computer with crap by default when you can have a one button purchase/install/update/manage for your apps.