Well your also hardware locked. The last time I worked on a mainframe (about a decade), 8 mb of RAM was $1000, a network card was $800. Commodity hardware around the same time 8mb was probably $50 and a network card even a good one was most $100.

You're paying a premium for both the hardware and the lack of develops knowing EBSIDIC, JCL, Cobol, etc..

Actually, from what I remember of Oracle, that might be very similar. I remember having to pay license fees per core.