I think your final point is actually exactly what Dave is saying. His point is not that everything should look the same. He's saying that it is helpful for common items, such as menus, to be factored out into reusable bits like Bootstrap so that we aren constantly reinventing the wheel.
Take a look at Mac programs, for example. For the most part, they all have menus, windows, and title bars that look the same. But the important parts of many apps are unique. This makes things easier for both developers and users.
Imagine, as a developer, having to code the entire UI from scratch every time. That's how it used to be. It's not so nice for users when every app looks similar but it subtly different. It means every app has a steeper learning curve.
I think there is room for both uniformity and creativity to co-exist.
Actually it is good when things that do the same things in different apps look the same. How would you like it if every car you drove expressed some inner esthetic of a designer in the way the steering wheel or brakes worked? They don't and for good reason. The utility of the product matters much more than the ego of the designer. I know it's hard to understand this, I had to go through the same thing when I was doing my first Mac product. Eventually I came to accept it, and then it made a huge difference in the economics of the platform. Because the apps had factored the common aspects of their personalities, people could use more apps. This made the market much broader, and made more developers rich. That was also a good thing for developers. :-)
This is what change looks like. Every generation of programmers wants to hold it back. It's not fair that you've invested all this in learning how the current layer works, well now it's not current anymore. You have to adapt, or you end up obsolete.
Younger developers always say this to the old developers. It's a bit disturbing when you hear it for the first time, about you. :-)
> > An OS UI is mostly buttons and other widgets, window frames, and behavior. The actual applications are very different.
> So is Bootstrap.
While that's true, it's a bit disingenuous given the difference between web development and native client development.
Not using Bootstrap doesn't mean that you need to write your own functionality from scratch; for elements like buttons all Bootstrap gives you is some nice CSS styles and a little bit of syntactic sugar over using the web browser's built-in implementation. There's a bit more of an argument for the JS plugins (tooltips, modals, etc), but even then the alternative is grabbing one of the countless other JS plugins that do the exact same thing, not necessarily rolling your own.
Yes, bootstrap is a good thing. But it should be used only as a base for further improvements.