Re: I'm impressed
Easy, most people are too lazy to actually read the documentation.
Its a bit more justifiable when you know it is documented somewhere but not which particular document set you have to look in.
And yes documentation (and some test teams) are often the people who get the biggest picture of how a complex system/application works. Most other people are too low level (concentrating on one particular component), or too high level (understand the architecture but not implementation details).