CSS reset is worse than any default browser style: in browser paragraphs are separated and lists have bullets. With CSS reset, there are no styles at all, and the page looks like unformatted text.
Browser default styles aren't really good enough to be usable IMO; yes they have paragraphs but with zero margin and tiny text they're not exactly readable. Twitter Bootstrap is pretty much a bug report against the browser default style. Given that current browser default styles are half-assed at best, I'm sympathetic to the idea that not having a default browser style at all would be better.
The whole point is to make everything look the same across every browser in existence. Also to remove collapsing margins.