Apropos and the like could also be a lot more perceptive if they only worked for one language, but it's a major trade-off. On this computer, apropos is a uniform interface to search all the BSD userland utilities, the C, Perl, TCL, and Erlang standard libraries, system design docs (e.g. hier(7)), etc.
Come to think of it, apropos could also search Haskell functions by type signature -- Haddock would just need to generate stub man pages for them. (I don't use Haskell anymore, but someone might find it useful.)
Incidentally, the pipe-able Unix utilities are so useful because they all have the same type (line-buffered text stream -> line-buffered text stream), which is a particularly easy one to use across languages.
Come to think of it, apropos could also search Haskell functions by type signature -- Haddock would just need to generate stub man pages for them. (I don't use Haskell anymore, but someone might find it useful.)
Incidentally, the pipe-able Unix utilities are so useful because they all have the same type (line-buffered text stream -> line-buffered text stream), which is a particularly easy one to use across languages.