"What the Mac realized is that there are a set of things that all software has to do, so why shouldn't they all do them the same way?" Indeed - but I'd venture

"What the Mac realized is that there are a set of things that all software has to do, so why shouldn't they all do them the same way?" Indeed - but I'd venture that the standard behavior for most web elements is already well-established. Pretty much everyone knows how to use a dropdown or a modal. Bootstrap makes it easy to implement these, and that's really handy. You could do the same with jQuery plugins or CSS snippets, though it would take more time. The bigger aspect of Bootstrap (IMO), and the one that really grabs people's attention, is its distinctive and consistent styling. That's what shouldn't be kept consistent across websites. (It's not like different styling will confuse users.) Tangentially, overriding Bootstrap's styling can be a bit messy, especially if you aren't using Less/SASS; but it's necessary if you intend to design a site with its own look. That's what I'm dealing with now.