Yeah but I'm sure Katy Perry gets enough out of the service to pay it $10k a year. For example.
Total revenue would be lower, yes, but that should be matched by cost-cutting. These companies' head-counts are bloated compared to the services they offer.
I know there's a lot more to Twitter than the simplistic short-messaging system it seems to be from the outside (speed, scaling, etc)...but does it really need over 4,000 people to run it? I highly doubt it.