I really want to see Ebert's televised interview before commenting on that further, but for me, I don't think the treatment of Rossellini was the primary issue Ebert took with the film. That was just one of many things wrong with it. What it all comes down to is narrative, really. If a film is advertised as such, it should be. Not that I have anything against more abstract films, it's just that Lynch's style in the two films I've seen is really annoying.
Mulholland Drive and Blue Velvet were both hypnotic and mesmorizing for the first two acts, but they fell apart, because Lynch draws on his own experiences and dreams, throws them into his films, and expects that to be a sufficient way to tie things up, when really, we're wanting not so much a valid explanation or justification, or even a closure, but simply something that gels.
Some writers say stories should have a beginning, middle, and an end, not necessarily in that order. That may or not be sufficient, depending on who you ask. I think something can be accomplished in film even eschewing that. But Lynch was just careless, and that's what I believe Ebert is getting at. And if not, I know at least I sure am.
EDIT: Lynch's dreams and experiences don't mean anything to us, and he shouldn't expect them to. Perhaps he should save those for his paintings, or at least gather his thoughts to make the images he's found in his subconscious more relevant to what he's discussing. Lynch's films (again, the two I've seen) don't really have a point other than to provoke you. And that, too, is careless.