Low-level API design problems are usually of the form "this API is hard to use". For example, XHR. This is (a) work-around-able, as any developer who's used XH

Low-level API design problems are usually of the form "this API is hard to use". For example, XHR. This is (a) work-around-able, as any developer who's used XHR successfully knows, (b) fixable, as witnessed by the numerous libraries that are better versions of XHR. High-level API design problems are often of the form "there's no way to make this do what I need". That's what Yehuda's blog post about AppCache points out, and the result is either building something less good, or not building things on the web at all. That's much much worse.