Site Reputation Abuse and Web 2.0 Site Builders

I understand that the primary motivation of this update was to crack down on sites like OutlookIndia, but aren't subdomain website builders doing something similar in principle (ie allowing third parties to publish content without oversight)?
I'm curious why web2 subdomain sites are exempt from 'site reputation abuse'.

I suspect most web2.0s offering subdomains are already covered by a different filter/dampening factor. Plus, most of the 'site reputation abuse' (parasite) stuff is going on in subfolders rather than subdomains.

I think subdomains are treated as an entirely separate domain.