Domains and sub domains DO in fact help with
SEO if the content is COMPLETELY relevant. However honestly if you are marketing correctly, it really matters little. You can get on top of search engines regardless of your url!
Its not on "top" of the search engine but if you do a google search for "blogs vs websites" (without quotes) I am listed in the top 30 results regardless that my domain name has NOTHING to do with it and the url in fact has a ?p=xxx without ANY targetting.