Whilst his point is intrinsically flawed, there are some valid (and scientifically proven) elements.
For example, it has been shown that a society that practices memory over recording has an intrinsic ability to remember things better -- like many organs, the brain's ability to work is increased by practice. Look at Bardic societies -- Homer's society was illiterate, yet he managed to stand up infront of a crowd and recite a whole book of his work. Writing is a form of technology.
Now, because we have technology to help us, I bet you'd find that theory translates into a lot of ares: Whilst we may still be as 'intellegent', we may not have the same ability to do things: math on the top of your head, remember your dates, ability to tell the time, etc.