The punchcard system surprised me, but I've seen plenty of Apple II and C64 systems used as standalone in small businesses, and various minicomputers are quite understandable (although most of the normal environment VAX stuff got moved to Alphas in the 1990s, which aren't that horrible from a maintenance perspective).
IBM seems to have a penchant for that, their series i computers run software written for even the previous system/36 and system/38. The i relies on a Technology-Independent Machine Interface to allow the hardware to change without requiring code changes at the software, for many release upgrades user written code simply is recompiled when the upgrade is done without source being needed or user action.
Yeah, the backward-compatibility lengths that IBM goes to are something amazing and wonderful to behold. I think a lot of developers these days don't appreciate the crazy work that into supporting bytecode from before they were born.
IBM's penchant for providing bit-and-millisecond-perfect reverse compatibility back to the 60s is built on the fact that their customers will pay very, very, very high prices for it.
I used to work for EDS (now HP Enterprise Services) about 6 years ago sub-contracting for Xerox. Most of the systems they (Xerox) used for selling/maintenance (order processing, invoicing, etc) of printers were written in COBOL for the IBM System/360 mainframes (which I think were replaced by the System/Zs).
