Where can I see Hokusai's Great Wave today?

I can see and appreciate Michelangelo's "David", in one of its two best-known Italian renderings (not counting the one in Las Vegas), even though the sculpture's human model, and the artist, are long dead.

I think Banksy has the right idea, even though people do what they can to undermine his works -- by, among other things, chain-sawing them out of the walls the artist chose to make his point, then offering them for sale.

A copy of a book isn't a travesty, so why should a copy of a painting be one?

This is because of how humans appreciate where the spirit of a work is. In case of a book, most of the essence is in the words, not in the paper or the ink - although, people do appreciate the print itself too to a great deal. But because the words carry the most meaning, the work gets copied, translated, even modernized, and agreed to not lose much of its meaning. After the mass printing era, there is no such thing as "a single master book" when referring to a work. There can be drafts, a manuscript, generations of copies referred to as different editions, etc. It's a mass production affair with a blueprint and products, whereas in case of a painting, there is a single, final version original usually, and subsequent reproductions are copies and modifications of that.

The other thing is that a copy of a painting is not a travesty at all. Many appreciate and decorate with replicas, prints, view them online, use them as wallpaper on their device, etc. I don't think people think of any of this as a travesty. The issue here is to present a copy as the original, in which case the replica becomes a fake. This is a lie, and a betrayal, and these evoke strong feelings in humans.