Oh, I agree it's not unique of train stations. The Japanese overstaff pretty much anything - it's likely part of the reason for their massive public debt, but it helps maintaining infrastructure to good standards. It's the opposite attitude we see in most of the Western world, where public resources are cut to the bone until (and often even after) things rot and fall apart.
JR East covers not only metropolitan train services in Tokyo but also a wider real estate/retail portfolio and all of eastern Honshu, with about 46k total employees.