Well, it's not that important anyhow. I mean, if you ERR an URI, and the web server doesn't log the request, no one knows about the ERR. No harm done. What Atom, and the rest of the XML community would do, is spread the word about ERR and try to get it into an RFC as an amendment to HTTP. As Hentry wrote, this problem isn't only with Atom, but with all XML on the web. All.
We need some kind of standard error reporting mechanism. XHTML served as 'application/xhtml+xml' needs it maybe even more than Atom. I think that if we go together, define a good spec for this (it would be crazy if it were on more than 2-3 pages total) and then spread the news about it, Apache and other web servers would have support for it in not so long time. And in the meantime of no support, ERR request will at best be logged or handled by custom HTTP handlers, and at worst not handled at all.
And that Atom is capable of doing more has yet to be demonstrated (to me ;).
I love the format inside-out, but I almost agree with you. The specification already gives probably ten times more than both of the RSS specifications together, but the sole formats alone don't give much from each other. They all do practically the same thing. That's why I think it's important that Atom has e.g. threading support in v 1.0, so that it actually has something to brag about.
cheers Bill