According to Google's latest announcement they've made significant changes to their search Algorithm with is estimated to effect roughly 35% of searches and better determines when to give you more up-to-date relevant results for these varying degrees of freshness.
"Search results, like warm cookies right out of the oven or cool refreshing fruit on a hot summer’s day, are best when they’re fresh. Even if you don’t specify it in your search, you probably want search results that are relevant and recent.
Given the incredibly fast pace at which information moves in today’s world, the most recent information can be from the last week, day or even minute, and depending on the search terms, the algorithm needs to be able to figure out if a result from a week ago about a TV show is recent, or if a result from a week ago about breaking news is too old."
Recent events or hot topics. For recent events or hot topics that begin trending on the web, you want to find the latest information immediately. Now when you search for current news likethe news Jams Bond film "skyfall", you’ll see more high-quality pages that might only be minutes old.
Different searches have different freshness needs. This algorithmic improvement is designed to better understand how to differentiate between these kinds of searches and the level of freshness you need, and make sure you get the most up to the minute answers.