Duncan:
I don't know for *sure* what the reasons to charge for the digital copy are, so I will answer as if someone asked me for my reasons.
Like everyone else, I only have 24 hours a day. My time is valuable, not free.
And if you have a collector's item, which I'm sure this owner's manual is, one has to take a lot of car in order to preserve the value of the item when digitizing it.
If you have *any* experience with scanning documents at all, you will probably agree that scanning the documents takes time and is work. Then you need to correct/photoshop the digital copy to make sure everything is clear as it's supposed to be. If I'm not mistaken, Robert then runs the documents thru OCR to make the digital copies more useful, and the items easier to search for locate.
Maybe there's someone out there that is completely bored to tears and would welcome doing all that work for free.
Me, I find myself feeling super grateful that for less than 20 bucks I can get my hands on the items immediately, most of them cost less than 10. I waste more money than that on coffee.
Have fun,
-- Paulo.