I noticed that too, but due to the change in pronunciation over the years, I guess the phrase has changed its spelling as well. I see "just desserts" all over the place. This wouldn't be the first time. The correct phrase, "just deserts" is actually quite rare. It's good to see people haven't forgotten the original phrase, but I think to no avail, the phrase's spelling will undoubtedly change because of the pronunciation. At least the meaning of the phrase has stayed intact. Interesting read, and nice find.