Before yesterday, I had no idea the U.S. had that many diplomatic staffers in Russia. I guess I never thought about it, but if someone had asked me how many diplomats and support staff the U.S. had in the country, I would have guessed about 100, maybe 200 at most. Apparently 755 represents more than half of the approximately 1200 people the U.S. had there. On the other hand, I obviously have little idea of how many people are stationed in an important country like Russia, not to mention the vast nation that it is.
(I guess the vastness isn't that much of an issue. The U.S. just has four diplomatic offices in the country, an embassy and three consulates. By contrast, the U.S. has ten in Mexico, six in China, seven in France, six in Brazil, etc. I wonder if those others are as highly staffed as Russia.)
UPDATE: The WaPo has an article explaining what those 1200+ people working for the U.S. in Russia do.