After having this service for roughly a year now it occurred to me that I haven't gotten many scheduled downtime emails. Maybe none at all. On my previous VPS I know I had to do operating system patching for security which caused some down time. What operating system and version are these WordPress installations on? How often are you guys patching and how is that done without downtime?
I have some limited info on the structure of Managed WordPress hosting. They're Linux based, but I'm not certain what specific system/version. They are also hosted by clusters of servers, so one server can be taken out of rotation at a time to be patched, without impacting site availability.