The userland shell isn't even a core component on either Windows or Linux. It's entirely independent of the kernel (the actual core of the system). If you so choose to do so, you can completely work from CLI. You can do away with Explorer entirely. This goes for any system. As to why Windows doesn't have software repositories is exactly what you pointed out: licensing. In theory, GPL/BSD/WTFPL software could be added to a repository for Windows users, but someone would need to maintain it. Microsoft obviously has no inclination to do that, and that's where it and systems like Linux differ. Linux is community driven, and software repositories are incredibly simple to setup. Since the majority of software is open source, anyone can modify something on a repository, add it back, or fudge it and create their own. Another thing about Windows software is that it can be easily infected. So someone trustworthy would also need to run these repositories. If you think about it though, they technically already exist. You've got sites like FileHippo, Softpedia, CNET, etc. that provide software archives and downloads.