There are a ton of high-traffic websites out there that don't need an architecture any more complex than a standalone DB server + PHP + varnish (or the equivalent).
More so, if devs spent as much time tuning the performance of their apps as they did fantasizing about "web scale" architectural pivots they would typically be farther ahead. StackOverflow.com is a perfect example of this. They run on tiny handful of windows machines, support gobs and gobs of traffic, and have absolutely fantastic performance. And as much of that is due to paying attention to performance and making sure to find and remove the bottlenecks where they exist as it is to using cutting-edge architectures like database sharding, map+reduce, eventual consistency models, etc.
More so, if devs spent as much time tuning the performance of their apps as they did fantasizing about "web scale" architectural pivots they would typically be farther ahead. StackOverflow.com is a perfect example of this. They run on tiny handful of windows machines, support gobs and gobs of traffic, and have absolutely fantastic performance. And as much of that is due to paying attention to performance and making sure to find and remove the bottlenecks where they exist as it is to using cutting-edge architectures like database sharding, map+reduce, eventual consistency models, etc.