I knew that the CGB allowed you to pick among the hardcoded 12 color palettes (by holding down various key combinations at the Nintendo logo boot screen), but after reading the article I was curious about this as well. I wonder why they decided not to make the CGB recognize the SGB palettes?
Because SGB palettes weren't intended to be used on the whole screen at once (or, at least, you couldn't assume that they were intended to be used that way). What looks great on one region might look terrible on the entire screen. So they decided to simply set it up so that if you wanted to make a palette available on the whole screen, you could do so by making a CGB version of it.
Interesting article, though. It would be interesting to see more games designed this way, though I doubt that'll ever happen. Pity, that.