Wow, lots of lovely paintings. Interesting, however, I see no actual bokeh. Perhaps lower contrast in color and tonality, a bit less definition in the edges, or a creative "debeautifying" of the elements as they get deeper in the frame in La Gioconda (If I may be so bold as to try to rationalize any aspect of these paintings).
I think that David is right on that lack of DoF in paintings might be due to how incredibly hard it must be to achieve realistic bokeh. Even with some current sort of spray painting tool, it would be very hard. Could you imagine having to paint a daisy with just enough definition to recognize it? Or a little bit more out of focus so that all you can tell it is a white flower?
Looking at Karl Connolly's "Depth of Field" I see the attempt at blurring the soil, yet no attempt at blurring the sky and the ground together with a technically incorrect horizon line which would be -exponentially- harder. It is a good idea to make your subject that which he chose.
I bet something with more detail has been done before, probably by someone in the times when painting was "cutting edge" back then people put so much more emphasis onto the art, so the rewards were higher as well. However, I also bet people might have thought they were "bad paintings", or a cheap attempt by the artist to work less or something... It might have been hard to convince the guy "paying your bills" that you really should devote the amount of time it might take to master the technique when he would have had a hard time convincing his guests that it was in fact a work of art and not a mistake.
You would also have to paint based on your peripheral by focusing on a guide if you wanted repeatable bokeh. That would be a pain. Or maybe by focusing on a thin strand of cloth.
I would love to see more paintings with shallow DoF. Interesting.
David, after seeing your last post I would mention that it is interesting how there isn't even the slight DoF achievable by our eyes when focusing on a very close object with far deeper background. This is the omission I find interesting. Even in Karl Connolly's "Depth of Field" the horizon clearly should be far more out of focus to be technically correct. Though the closer soil just behind the rock probably shouldn't... unless the artist "cropped into his eyesight" for interpretation -and decided not to attempt the horizon line.