'Built-in' does not mean, hard coded words, it means giving the user ability to use that function, so you are able to add your own words.

Just like, for example, your NOTIFY list, Khaled isn't going to say 'Bob' must be in your notify list by default, and should you not like the idea of NOTIFY, simply don't add anyone to it and you won't be bothered by it.

And, yes, they are filtered out as a predefined (by the user) set of letters, however, a word is not a word unless it has spaces either side.