It's a lot more of a hassle, though, to ask users to keep an extracted directory sitting around which Chrome basically symbolically links to, than to just download a .crx, drop it on the extensions window, and then delete that .crx.

Even I still get confused sometimes, as a chrome-app developer, when I move a project folder and Chrome suddenly can't find my extension. It goes against how we think of "deploying to test" in any other development workflow.