>Their hardware is of higher quality, but I think their uptime has more to do with the hermetic seal of human process that exists around the installations. You can't get anything changed in production, ever. And thats fine, because banks have been doing the same thing for the last 30 years.

You hit it. Things break when you change things. The high priesthood that surrounds all mainframes prevents that from happening.

Nowadays, if you have to change stuff, IBM sells you AIX boxes that cost nearly as much as mainframes which sort of integrate with them to support those changes.