Plus it's been out for longer than its development cycle (14 years).
Has anyone noticed how literacy is just as much taken for granted in the Mojave as in a developed country? We know at least some of the Three Families can read because Cachino keeps a journal and someone is updating the sign outside The Tops with new acts. So who taught them? The securitrons? If they were warring tribes up to "a few years ago" (the loading screen says "a few decades ago" but there's no way Benny is that old)I can't imagine they were passing down the written word to their children.
It's not even so much that everyone can read - you could probably come up with an explanation for half the NPCs in the game. It's the fact that everyone assumes that you, a complete stranger, can read and keeps handing you notes and such. The only one who doesn't and takes precautions is Elijah, of all people.
I know it's petty, but since Bethesda Fallouts are criticized for having unreasonable/unexplained living conditions, it seems only fair to point it out. Also sorry if this has been discussed already. Searching this thread for "literacy" just brings up posts about media literacy.