Compare the community to something like Guild Wars 2 - obviously the game community with which I've been most involved. GW2 has a whole myriad of media circling it - official and unofficial blogs, numerous active forums and reddits, Twitter feeds (concerning news, lore, fansites etc etc) and podcasts. FIFA, conversely, has only a few fansites (sparsely updated), a few twitter feeds, little interaction with the developers (they are EA after all) but perhaps the most active and vibrant element of the FIFA community are the YouTubers.
For Guild Wars 2 we've obviously got some big YouTubers (Woodenpotatoes, MattVisual etc) but they mostly act as news/opinion sites. The FIFA YouTubers, for a lot of people, are venerated as deities. KSI, perhaps the biggest of the lot, has recently been on an international University tour and has attracted massive crowds just to come and have the chance of playing a game with him.
1) On 11th October 2013, KSI posted the following video:
The outcome KSI posting this simple two minute video is that EVERY SINGLE PLAYER is now doing this exact method straight from kick off. 90% of the time it doesn't actually work, but whether or not it is successful is entirely based upon the luck of the draw, will your defender stand around like a numpty or will he be in the right place to head it away? Who knows, lets hope the luck is in your favour. KSI is just one guy, but he's managed to influence the play-style of 75% of the players of one of the most popular games in the world.
2) Another popular YouTuber Nepenthez, made short video "Easiest Trading Method EVER!" The general idea being "buy cheap Irish players a month in advance in preparation for the St Patrick's Day Cup, when their prices will drastically rise".
Now, it doesn't take a degree in economics to work out what happens if you flood a market with players which everyone has already bought a month ago. What actually happened is that almost everyone invested thousands of coins into Irish players, and almost all of them lost all that money because no-one was buying them. No-one needed to buy them! They were trying to sell their stockpiled players, not buy more! The whole thing was a debacle.
These are just two examples of the strange position of power held by FIFA YouTubers. I'm not really placing any blame on them, they're just doing their job, but a single video can crash the market or influence the play-style of the entire community, and I don't believe that is necessarily a good thing.