Why not include installation media? What's the compelling argument against it?
They cost money...
That argument, at least, I find compellingly unpersuasive. Apple is one of the most profitable businesses in the world, with greater market capitalization than any existing company save ExxonMobile and more cash on hand than any other company period. The amount of money those DVDs cost is quite literally below the noise threshold; a momentary blip on the world oil futures market that drives up the cost of shipping by a tenth of a percent quite literally costs Apple far more than those DVDs.
