Do you even know Cocoa? I do, and I can't even begin to explain how they did the linked code scrollviews comparing the diffs. Trust me: implementation was extremely complex.

I've seen the math behind it and you are definitely correct.

Could you please enlighten me?

In the fluid mode, the text on the two panes need not be of the same height given the insertions and deletions. So when scrolling, the scroll speeds for the two panes would need to be different. Is this what is being talked about?

I don't. I would guess though that the complexity being talked about is not coming at least majorly from Cocoa.