It may be the biggest change in the Google algorithm that very few people noticed. The reason they didn't notice is that the change has been slowly happening since February, 2011. Between Panda, Penguin, and the rise of social signals, word count of content is not something that you should ever focus upon when writing content for search engine optimization or social media marketing purposes.
Here's a quick breakdown of the loose timeline. One of the first changes that happened when Panda, Google's low-value content algorithm change of 2011, rolled out was that the total number of unique words in stories had a predictable affect on SEO value. Stories with fewer words were deemed less valuable. This lasted for about a month. I cannot say for sure how the conversation went at Google, but at some point in the early days of Panda Google noticed that there was some great but very short content that was being hurt, while low-quality content with a lot of words was getting favorable treatment. This is where links and social signals started making a quick comeback into the realm of understanding the importance of a piece of content.
The example in the image above is what Google likes today. That's not to say that they don't like long, comprehensive content, but in the case above an infographic with a coupe of paragraphs of content but strong social signals to the page was able to easily trump much longer pieces of content on the same subject. It ranks exceptionally well for the target keywords despite the lack of words.
The content that you post should have a purpose. It should then fulfill this purpose in as few words as possible. This is a dramatic change from the days of old in SEO where more was better. Now, quality trumps quantity (as it does in so many other ways and in other arenas) to the point that giving your readers what they need without loading it with fluff is ideal. They will be more likely to share it, to link to it, and to interact with it if it's something that fits into their schedule. That's not to say that you should only write a couple of paragraphs on any subject and call it a day. It simply means that you should write your content to fit the need, to fulfill the goal, and to become a resource for your readers.
It's quality that makes the difference. You're better off focusing on a topic that is important and of interest to your readers, then bring the value to them quickly.
I do not want to be misunderstood on this: if a topic needs 1500 words to cover it properly, then write 1500 words. The point is that if a topic takes 300 words to cover it, don't think you have to fluff it up to any of the "magic numbers" like 500 words for it to be valid to Google. It doesn't. They know. It's better to have a short, concise, and valuable 200 word article with a graphic that gets shared on Facebook, Google+, Twitter, Pinterest, and other social sites and that people are willing to link to from their websites than to have a piece that's fluffed up to hit a particular word count.
Write what you need to write, no more, no less. Focus on quality and get the concept of word counts out of your mind for good.