According to them, Microsoft's Windows Updates had absolutely no downtime in recent history, Apple had only a few hours of downtime and Ubuntu, currently the most popular desktop Linux distro, had nearly two days of downtime. An interesting perspective, but one that I feel is skewed. The data was retrieved by a company called Pingdom who polls the update services all day long. There are a few things to consider when looking at the data, however. For one, Ubuntu's update service, like many Linux update services, is based on a system of mirrors – if one mirror fails, there are still others to take its place. It is unclear if Pingdom took this into consideration. It seems unlikely that many mirrors would be down simultaneously.
Another thing to consider is the length of time it takes to push security updates out. Microsoft has always put themselves on a fixed cycle, hence why so many of us are familiar with “Patch Tuesday”. Other operating systems do not take this approach and can issue updates more frequently than that. Scope is also a consideration. Windows Update is reserved solely for system updates, whereas other update services like System Updates through Apple will apply updates for hosts of programs, not just the OS and an office suite. Still, Microsoft does deserve some credit. When the vast majority of installed PCs are running Windows and no doubt thousands of installations occur per day, making sure your update servers are available around the clock is paramount.