Besides what account42 noted, two more things: - Have to consider the domain is a string, not a hierarchy. Too many premier domains have had subdomains with sp

Besides what account42 noted, two more things: - Have to consider the domain is a string, not a hierarchy. Too many premier domains have had subdomains with spam, malware, etc., running on some random thing in their namespace, trying to draft on the domain rep. - Legit traffic + comment forms + web links are a thing spam and adult "se.xx 2nite?" bots target. They seek out the ranked traffic to boost their clicks and good rep to boost their SERPs, so -- perhaps counterintuitive -- scoring traffic + rep as an indicator (to be combined with other indicators of course) is sensible.