There is one major exception to the rule of thumb that pretty much all throws that you ever see are from the Divine Nine. Uchimata is the most successful throw that is thrown in judo competitions. So, why didn't I include uchimata in the 'Divine Nine' list of judo kihon? It's not kihon because: 1) It's a variant of ukigoshi, 2) it is harder to learn than anything in the Divine Nine, and 3) it is harder to fall from than anything in the Divine Nine.
This brings up a pretty important point when you begin trying to define a small set of kihon for judo. You can't reduce the whole system to these nine throws. Not only do other throws, like uchimata, comprise a significant portion of the opportunities for throws, but sometimes it is specifically the threat of some of these other throws that make the Divine Nine so easy to throw. If you have to watch to make sure the opponent doesn't get you with 40 possible throws, you tend to leave about 9 holes in your defense. When you try to plug some of these nine holes, like stiffarming to stay out of osotogari, you make bigger holes for other throws.
So, while the Divine Nine are representative of all of judo, and as such are worth some practice time during every class, they are not ALL there is to judo as a system.