I have an RHCE so I have some experience in what you're optimistically calling a real operating system.  I will state that Linux is not yet on par with REAL operating systems like OpenVMS (or MVS).  I've been managing OpenVMS systems and clusters for about 25 years.  My current cluster uptime is pushing 9 years - that's 9 years of continuous availability in an active/active multi-node, multi-data center cluster.  During those 9 years, every one of the original systems has been replaced and the replacements included architectural changes from 32-bit Vax to to 64-bit Alpha.  The entire storage system was swapped out, including the boot disks.  We've had multiple single data center outages.  Individual systems have been rebooted multiple times, operating system upgrades were done, but in all that time, the core applications have *NEVER* gone down.  And I don't even hold the record for uptime - that goes to Irish Rail where the cluster was up for over 17 years.  Search HP's web site for their disaster recovery video where they blow up a data center (natural gas and a spark - and I do mean "blow up"!) and see how long it takes each environment to come back online.