Looking over the comments on HN, people seem to be focused on the current popularity of Twitter Bootstrap and Flat Design, but the original article posed a more general question across decades of web development. Just counting the last few design cycles, we've seen (1) web 2.0 rounded corners and gradients, then (2) iOS-inspired skeuomorphism and now (3) flat design.
People redesign websites to avoid looking "dated" and copying what's currently popular is the quickest way to achieve the look of "newness". The same is true for a new website built from scratch. Nothing is preventing someone in 2013 from designing a web 2.0 website except for the fear that it will make them look old. And if you're a business, you don't want to lose customers because your competition has a more modern looking site. As a result, everyone moves together as a pack in the same direction until someone else comes out in front and changes the direction of the pack. This is how culture has operated for thousands of years. Twitter Bootstrap is not the reason why everything looks the same.
> Twitter Bootstrap is not the reason why everything looks the same.
Except, Twitter Bootstrap filled that niche of a semi-generic framework distributed with a 'good-enough' design theme. In the web world I can't think of an example before. There were Wordpress theme frameworks that came without design and expected you to craft your own, and there were good designs created without thought for adapting the code.
Nothing said you're not a designer, but build with this and it'll look good before.
Now whether the 'Bootstrap look' became popular because of Bootstrap, or Bootstrap was buying into a design trend that was just starting I don't know. But both trended at the same time.
Really, what we are saying when it comes down to it, is that design choices are a form of communication. Staying 'modern' with your design is a decent shorthand for communicating a certain level of competence to your audience. I do wish that designers would look at it more broadly though. Perhaps it is not fair to compare web to print since print has had a longer history to draw from, but one of the things that I appreciate about print media is there is never just one 'go-to' style so fads don't get as tiresome because they rarely are pervasive.
People redesign websites to avoid looking "dated" and copying what's currently popular is the quickest way to achieve the look of "newness". The same is true for a new website built from scratch. Nothing is preventing someone in 2013 from designing a web 2.0 website except for the fear that it will make them look old. And if you're a business, you don't want to lose customers because your competition has a more modern looking site. As a result, everyone moves together as a pack in the same direction until someone else comes out in front and changes the direction of the pack. This is how culture has operated for thousands of years. Twitter Bootstrap is not the reason why everything looks the same.