Windows 10 duly got its official launch this week, in an event which reflected the critical importance of the operating system to Microsoft – but was light on the mobile vision which will be essential to its success. In the age of open source and cloud services, Microsoft has a significant challenge to keep an old-fashioned OS relevant, even if it makes it free to most consumers and partners over time. CEO Satya Nadella has robust fallback plans, notably to deliver key applications from the cloud to any OS, but he has one last chance to control the end user experience via a new take on Windows. That relies heavily on the OS being able to run on all kinds…