Only, our brains look no different now than they did two hundred years ago. For that matter, since the appearance of the first homo sapien sapiens, there has been no change in capability.
Culture has changed: technology, communication, language and with them philosophy, behavior, and taste. It makes sense that in Old English it was proper to say 'aksed' and that a child in the modern American school system is chastised for the same pronunciation. "Proper language" shifts, just as all things do.
If that is the case, the definition of "good writing" is a recognition of the preferences of the era. They will evolve and shift in response to "groundbreaking" works respected in the writers' circles.
But best sellers aren't necessarily concerned with quality. Often it is the ability to master character which draws the populace to reading these books, but the reactions readers have to these characters further illustrate that it is all a matter of preference. For instance, I read a blog post discussing Twilight. The author of the post enjoyed the book and attacked those who dismissed it as bad writing. The one point of contention I have is with the the analysis of Bella. The blog author likes Bella's character because she believes it to be realistic. Obviously, plenty of readers agree. I personally, don't care if it is realistic. I don't read a book to get as pissed at the characters' whining as I did with my fellow teenagers in High School. When I was in high school, I read to be exposed to something more. Yes, a bit of escapism was essential then and it still is now. Which means that I want to identify with my characters, but I also want to like them. Who I like in real life and on the page amounts to my own personality and taste. When encountering characters we bring our own histories and baggage to play, our own perceptions of reality and our own preferences. So taste enters the picture.