Relative links for media

Is there a good reason why WP insists on creating fully-qualified absolute URLs for IMG tags and links when you add an image to a post? This makes no sense to me – why not use relative links, since we know the image will be on the same domain as the post that references it? Yes, I can manually change the references to make them relative but that’s a pain. The reason I care is that all these absolute URLs make it so much harder if you want to move or replicate your site to a new domain.

I’m also aware that there are plugins that help you convert existing URLs to a new domain. That’s nice, but why do we have to go through that hassle at all?

Is there a plugin that overrides WP’s behavior and makes all internal img tags and links relative to the current domain?