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Not exactly: last I heard there were many more "readers" than "fen". Fen are the ones who make fandom the subculture that it is, whether they're in the "fandom is just a goddamn hobby" (FIJAGDH) camp or the "fandom is a way of life" (FIAWOL) camp or anywhere in between -- they're the ones who maintain enough connections for there to be a community of F/SF fans, go to conventions, filk, etc. Most are readers, some are "media-fen" (which means telly & movies), and a rare few just like the community/subculture and aren't really all that interested in science fiction otherwise. "People who like SF" would include a lot of people who quietly enjoy the genre without particularly connecting to others on the basis of that. (And as I noted at the start of this comment, I think they greatly outnumber us fen, though it's possibly that my information is out of date.)

I used to work with two science fiction readers who didn't know each other liked science fiction until more-obvious me came along. It's unlikely that two fen working in the same place would've failed to notice each other.