Earlier quoted context omitted.
"you aint gonna need it" can be clarified as "you aint gonna need all those extension points". it can also mean you don't need functionality you're not using, including implementations for those extension points.
While I accept your definition, because, hey, programmer's can't agree on definitions at the best of times, that is not the definition that was used earlier. And is not the definition presented by the XP gang. John Carmack of Doom fame seems to share your definition, suggesting that attempts to plan architecture in advance will only come to bite you, but I'm not sure he is an XP subscriber and he certainly wasn't inv…
It's a mis-interpretation and it's not a reasonable one either.