Google search results treat subdomains as Folders - 2 Results per search Per Domain
Thats the new buzz in the Google new search filter, which is now treating sub-domains as an integral part of the parent domain and will only show 2 results per domain in the order of relevancy and will not show as many results as their are sub-domains.
Google - 2 Results per search per domain
In the early days webmasters used to create multiple sub domains and used to rank their web pages by deriving an extra mileage from the relevancy of the parent domain, but with this move from Google this tactic technique will be put to rest.
Also this step from Google will push the Webmaters and SEO experts (who have used sub domain as a part of their SEO / marketing strategy) to bring about considerable changes to be more effective.
What drove Google to take this step?
Webmasters and SEO were spamming the search results by using the relevancy of their parent domain to include more pages from their website by using sub domain, which gave Google enough reason to apply this filter.
Along with this the basic terminology of having a sub domain is to create a website on a different topic, so if Google is implementing this as a filter its not wrong in any way.