It's the same model that both Apple and Microsoft use for their OS updates, especially when upgrading from "dark ages" version to the latest version. I just think that most Linux distro providers either don't have the resources or the passion for Windows programming to make & maintain the windows .exe part of the pathway. Wubi is neat, but living out of a file on an existing partition doesn't feel like a pathway to full-time Linux. But if it already exists and is maintained, why hasn't it become the standard approach for all distros?