Web manual pages are not giving sections

I wanted to use the web manual pages, but I cannot get the correct sections.
For example, if I want to browse all the intro's, only a few will come 
up, even if I use the link or the form

I can only get audio(4), not audio(9)

-- 
A human being should be able to change a diaper, plan an invasion,
butcher a hog, conn a ship, design a building, write a sonnet, balance
accounts, build a wall, set a bone, comfort the dying, take orders,
give orders, cooperate, act alone, solve equations, analyze a new
problem, pitch manure, program a computer, cook a tasty meal, fight
efficiently, die gallantly. Specialization is for insects.
    -- Robert Heinlein