Haskell also tends to also have a wide gap between beginner material and advanced material and not a whole lot in between. Some beginners will often come and see advanced discussions about the lens library for instance and will assume that they need to learn the lens library in order to program in Haskell. This just leads to disaster since it's nearly impossible for beginners to decipher the type error messages that come out of it until they grok the type system at a more advanced level.
Do you have any example were the documentation available is only scientific or technical papers? I've been learning Haskell for a year now, and even though I've read some papers due to interest I've never felt like it was the only form of documentation.
I could think of others if I dedicated some time to it, but those come up fairly frequently.
decodeUtf8 :: ByteString -> Text
There are also quite a few things that are thoroughly documented, sometimes not in the Haddock (which, there's some argument, should be kept simple like a reference). Yesod has a book, and I hear Snap's getting one.
There are certainly cases that both don't have thorough documentation and need it, but they're not as many as you imply.