[kevingadd]

I'm not sure you've ever used XHR if you call it the callback pattern.

The XHR object is effectively a request and a response bundled up into one object that has promise-like traits. You attach event handlers to it to handle various state changes and scenarios, and then once you issue the request, the event handlers get invoked 0-N times. If it really was JavaScript callback-style, XHR would look like this:

    window.xmlHttpRequest("GET", url, function (result, error) { ... } );

It doesn't. setTimeout/setInterval are definitely callback-passing, but they're not exactly glowing examples of stellar API design. They return integer IDs instead of handles or objects!

Honestly, the only way to classify node's callback-heavy design as a 'no-brainer' is if you excuse the design by saying no thought was put into it beyond simply doing what a bunch of other people were doing. If you put enough thought into how large applications will be built, and how difficult it is to build scalable, maintainable libraries, callback-passing style easily loses compared to promises.