de cuts everything from, and including, the character under the cursor up to, and including, the last character of the world, e is an inclusive motion.

dw cuts everything from, and including, the character under the cursor up to, and excluding, the next word, w is an exclusive motion.

The answer to your question is not in :help d ( de and dw are perfectly consistent with it) but in :help e and :help w ( e and w don't have to work the same because, as the doc says, one is inclusive and the other exclusive).