You asked why would God send down a book when most of the population were illiterate.....I pointed out that he didn't. He sent down the revelation verbally for dissemination. Who said the intention was for it to be stored, the revelations intention is to be spread, not stored and that can be done in a whole raft of ways.
God really should come up with better ways of getting his message across, for an omnipotent being he seems to be really rubbish at making a clear point...

