[chrischen]

Yes you still have to test your app on different platforms and browsers, but the point of the build process is that they make them work on those various platforms, whereas before you would have to manually fix those failed tests and hack in fixes for obscure conditions. That's what frameworks and libraries are for. They've abstracted away things so you can focus on higher level things. Tests are always going to be required, even if your framework and libraries are perfect.

We don't need to stay close to the platform because abstractions allow for more advanced applications. That's why most web apps don't use C, and should never use C, because 99% of the coding work is higher level tasks that don't need the bare-metal performance optimizations.