Randall, I guess you are naive.
The department that I work in with about 100 people support just ONE small area of a major company, and we have well over 50 million lines of Cobol and PL/1 using IMS/DB2 to support crossing maybe 50 systems of varying sizes and about 2000 modules - each very complex.
The complexity of the interfaces is mind boggling. Not to mention that the batch run that we do nightly would take about 12 days without a mainframe behind it.
I would estimate that the cost of completely re-writting just this small piece of the business would cost GM about 100 million dollars. But it WORKS the way is it - so WHY?
I can assure you that these will not be re-written in the next 10 years. They are putting some nice GUI front ends on them, and migrating
alot of reporting to shadowed data on Oracle databases, but Batch ain't moving during my career.