Earlier quoted context omitted.
btw Futurama's writers were paraphrasing this: "I think there is a world market for maybe five computers." Thomas Watson, president of IBM, 1943 (of course in 1943 that was a totally reasonable thing to think considering they were the size of a small house and ran on thousands of vacuum tubes that needed constant replacing and started in the millions of dollars)
And it’s come full circle because today the majority of the Western world’s computing needs are served by five computers: Google’s, Facebook’s, Apple’s, Microsoft’s and Amazon’s. Each of them consists of millions of individual devices, but the end user posting to Instagram or accessing their iCloud files doesn’t need to know any of that.
Even if you pretend the user has a dumb terminal, that's 5 computers that can each serve a hundred million users at once. Very very different from batch processing.
Also the original quote was about preorders for a single model in the united states.