This is one of those things that rankles me.
Every now and then, in a conversation with practitioners of other martial arts, I will run across someone who takes the attitude that everything that you show them was already embedded in their martial art. They look at Muay Thai and say "oh yeah, we already do that", or "there's grappling in our kata, really". My personal favorite was the guy who told me that his karate system actually contained everything that was in the SPEAR System, but I would have to study his system for fifteen years to realize that. Talk about an inefficent training paradigm.
The reason it rankles me is not necessarily because they're wrong (I admit to thinking the karate guy was, flat out, wrong, but it's arguable), but because they can't actually do the stuff they're talking about. In other words, kata may, in fact, contain grappling movements. The little bits of kata I remember supports the idea that you could use those motions in a grappling context. Which is nice, except that if you never actually grapple with someone, that fact is totally useless.
If you never understood something or practiced something until the moment someone from another system showed it to you, then having it "in there" wasn't very useful. It's a bit like having a gun that's kept in a safe, unloaded, a thousand miles away from you. That gun is pretty nasty, but it's unlikely to ever be of much use to you.