Lockheed is a horrible example too because they have extensive classified operations (their support costs for email within classified projects probably exceed 7.5mm alone), and because Lockheed IS&GS is a major contractor for outsourced IT services.
I think the Gartner figure was something on the order of $500-1000/yr per employee for messaging in large high tech businesses. A lot of that is IT staff, and all the other systems for security and compliance. Email is one of the big apps within enterprise.
Yes, I certainly do believe that any American corporation with 150K employees spends significantly more than $7.5mm/year on their messaging system.
These systems actually get _more_ expensive as they grow larger - Disaster Recovery, Business Continuity, Sarbanes Oxley, Customer Service, SLAs, Data Loss Protection, Intrusion Detection - All these email services that the small enterprise doesn't worry about (that much) - add up significantly in larger enterprises.