Although netcraft provides up-time for hosting companies - there is a lot that netcraft uptime rankings do not tell you.
If the update is reporting a Linux server, and you are running Windows, how does the company rate on Windows uptime and vice versa?
Although a specific box may remain online for a very long time, that means the box hasn't been rebooted and therefore security patches have not been properly installed in a timely manner - correct?
This uptime report tells you nothing about a company's internal security policies and practices, which some may find in terms of lost revenue to be more important than uptime alone.