I suspect that (with the exception of machines featuring licensed subject matter) the ownership of pinball machines is much easier to sort out than the ownership of many video games. There is most likely no "home port" rights to get in the way plus pinball machines weren't generally licensed to different companies in different countries. And there generally tends to be one entity involved in creating them. Plus tracing the ownership of the pinball rights from the big pinball manufacturers is generally not that hard. Oh and unlike video games, there is generally no prospect of a pinball machine making money via re-releases or collections or whatever.