That's the right sort of ballpark for the systems my team maintains. We don't run RHEL.
"Stability" in the RHEL sense is akin to ossification: you don't change anything, and then you can't change anything, and then you've got problems. The costs aren't necessarily as obvious as pursuing stability via dynamism, and in any case can often either be avoided by limiting the lifespan of the system as a whole or at least punted on to a successor.
For military applications, the trade off is even more intense: you build things hoping that they'll never be used, but knowing that they need to work when called upon. Stuff that'll be on the front line tomorrow can have a very different set of lifecycle guarantees from stuff that's got a planned life of 25 years but which (from experience) you know will probably still be around in 50.
We are at 500k/hour for at least one system i know of at my current client (energy). Not sure what causes these expenses. It can be missing out on trading, or fines. There may be more of these systems :)
