Safari is the only browser that has decent scrolling performance on a Retina MacBook. All the other browsers stutter really badly as soon as the page has any complexity with fixed elements (Facebook is a big one)
That's a case where Apple has to optimize the heck out of Safari until it is workable on that particular new machine, otherwise it would get terrible reviews and hurt the overall brand.
Chrome doesn't have the same incentives to get that particular machine working well, especially since the next revision of the Retina Macbook probably won't even need special handling since it will surely have a more powerful GPU. They can just wait it out, similar to what happened with the iPad 3 vs iPad 4, where people had to optimize for the iPad 3 and then those optimizations were unneeded on the iPad 4.