Why are iTunes updates so big?

[SideWinder]

So i have finally gathered motivation to update my iPod Nano, opened up iTunes and it needed an update fair enough. Why is it 77mb?

I swear it is always this big...why does it always need such a big update?

Or am i just downloading iTunes all over again rather than it simply being patched?

 

[SideWinder]

It isn't huge, no. But for an update? Hmm.