Why the Standard Library

[Zachary Lund]

I've been wondering in the back of my mind for awhile now and it 
really hasn't bothered me much but I figured I might as well get 
it off my mind.

Why is there a need for a default "standard" library? I can 
understand about some of the core stuff, but hell, even threads 
can be handled via a 3rd party library. Why must Phobos or any 
library be a part of D itself?

I'm unfamiliar with the reason for C++ having a standard library 
as well (which I bring up when people bitch about poor design or 
something similar which I usually get no viable or any answer at 
all). More of an ignorant question probably but oh well...