Matt's point is that they've chosen a system that makes it really hard to get that last 10%.

"We have tried to draw spirals using cartesian coordinates, what we have gets us 90% there, but there are infinities and edge cases involved in getting a perfect spiral. The equations describing them would get so complicated it's just not worth it."

What we have in BitKeeper is the equivalent of polar coordinates... it makes drawing spirals much, much easier ;)