I'm not trying to be a wise guy, but rather trying to understand where the spam part of this concept came from.
First, what is spam? Unwanted email or a site that represents other than what it is. If a site were named free-stock-quotes.com and it indeed gave free stock quotes, wherein lies the spam?
In the reference to the "weak" site, I was concentrating on two factors - it is smaller than the competition and has no real rank due to "who links to a auto air site"? However, it rapidly became number one in all three SE's. Why? Because the domain name matched the search and the content fit the domain name. Where is the spam in that?
To reiterate my question - where did the reference to spam come from? How does hyphenating two relevant words convert them to spam?
"....some SEOs have theorized it is a spam indicator which Google may consider."
I have evidenced superior results with hyphenated domains - not theorized or heard rumors. I also routinely see domains with low ranik and superior construction beat much higher ranking sites to the top. It's not all about rank
"A simple domain name has more opportunities to receive direct traffic."
That is entirely based on the quaint notion that peole know what and where the URL bar is AND remember your domain name too. That's why I use shortcut domain names - register the "search name" and put the short one on your cards, etc. I am amazed that I have to say seUP.net more than once. A short name is still no guarantee. Search results is what SEO is about, is it not?
AS MOBILES DOMINATE GLOBALLY - a domain name's function will be more like a scanned UPC than a phone number you dial manually.
(Half a billion people accessed mobile Internet worldwide in 2009. Usage is expected to double within five years as mobile overtakes the PC as the most popular way to get on the Web)
I still have yet to see compelling data that hyphenating a domain name is considered spam by Google, etc.
**"Google ranks domains with keywords in them highly, even if they contain hyphens"....Rand Fishkin
"...though I'm guessing part of Google's spam filter early warning system does look at hyphens"....Rand Fishkin** (...Google looks at everything and a hyphen is a thing. Google also looks at keywords - and punishes when you use too many [stuffing]. It is logical that hyphens are in the mix with a thousand other factors, being evaluated for use or abuse)