Knowing this, the good Mr. O'Reilley actually sells most of his material on-line, for electronic delivery, which of course makes a great deal of sense to him since they're all just DocBook files anyway.

If you mean "most" as in "most of the O'Reilly catalog is available through Safari", then that's mostly true.

It you mean "most" as in a quantified portion of sales (whether units or revenue), then it's not true.