Not really. I was just following your initial wording.
Actually, I'm most partial to underscores, but I think the value of both underscores and hyphens is dwindling, even in directory and file names. The algos are getting quite linguistically savvy.
Using hyphens and underscores to separate the keywords used to help significantly -- by helping the algo along by parsing out the keywords. But even now, they sure don't hurt, and I think they make the URL look more authoritative when that keyword is separated out in the URL on the returns page. More likely to draw the click, you know?
So I still lean toward the hyphen or underscore, rather than the run-on word. After all, not every search engine has cutting edge programming either. Some of the second tier engines still respond well to techniques that stopped working on the big ones a year ago.
Back when Excite was pretty normal(1 year ago)a lot of the sites listed in their index were sub-domains. We really thought that it had something to do with the keywords in the sub-domains.
We went nuts and set up about 600 sub-domains to throw out there. Since then, we have never had better results with sub-domains than the good ol www. They are all hyphenated. Works well when you want to put the domain in the title.
I think that people say it works because they spend so much time in trying to make it work. Then when it actually gets listed well, they just assume that it's from the keywords in the sub-domains.