Sometime Google fetch keywords ranking from meta tags but sometimes Google update title & description in search results from web pages contents.. I think it's all about fetching from heading Tags what is your opinion please share..
SEO meta tags and web page contents both are important now. Search engines check what you are defining in title must be in your body contents. No one know Google secret but i think google shows those contents in search results which are informative, weightfull and according to keywords (What people are searching for).
Bottom line, your content HAS to match what you're talking about, its got to be informative, to the point, and presented in such a way that your readers will want to consume it.