They do talk about the chicken and egg situation, where top sites will optimize for engines, then engines optimize for sites... i.e. it highly depends on the sites - of course all browsers test on top sites and optimize for them. But then the cycle repeats.
They do talk about the chicken and egg situation, where top sites will optimize for engines, then engines optimize for sites... i.e. it highly depends on the sites - of course all browsers test on top sites and optimize for them. But then the cycle repeats.