Well clarity != short/simple. Which is sort of the joke of the whole book/this idea. It can often take many more words (which just makes an idea more complicated) if you rely on this kind of idea (which yes, I'm aware is a joke) than just using the correct word.
It's also very possible to get the gist of a word, based on where it is placed and the words around it -- even if you don't know exactly what it means. (Obviously I'm not suggesting that for something like documentation writing -- but by the same token I would never think that limiting yourself to a 1,000 word dictionary for something as important as product docs would be beneficial in any way).
I strongly suspect there is a happy medium to be found. Maybe more than 1000 most popular words...and maybe just augment a limited dictionary with an addendum for technical terms not in the short dictionary, but that are extremely common for the subject. E.g. in my case, maybe "domain" isn't in the dictionary, but I obviously need it to talk about DNS. I would reasonably expect even foreign language speaking administrators to know this word.
So, it's a joke, but maybe a useful thought exercise, too.
It's also very possible to get the gist of a word, based on where it is placed and the words around it -- even if you don't know exactly what it means. (Obviously I'm not suggesting that for something like documentation writing -- but by the same token I would never think that limiting yourself to a 1,000 word dictionary for something as important as product docs would be beneficial in any way).