Practical English Usage   (Michael Swan)

about and on

compare :

-        a book for children about Africa and peoples. 

-       a text book on African history.

-        a conversation about money.  

-        a lecture on economics.

   We use "about" to talk about ordinary, more general kinds of communication.

 "on" suggests that a book, lecture, talk etc. is serious or academic, suitable for specialists.

( from mis.bitarafan )