Yeah, for images you can probably deal with that; but what if your JavaScript doesn't load because the script itself was a 500 error, or the entire website doesn't load because of a 500 error... well, you're screwed. The use case here is for zone-apex whole-site static website hosting (either of just canonicalizing redirects or of the final webpage: same issue).

I've just discovered that you can use the same technique for script and style tags too (though I'd rather not have to).

It sounds like Jeff has tracked down the specific issue in your case, so things are looking up :)