Well, at least in the United States it is a fact that many people take this situations very seriously. The most recent case was Tony La Russa, the manager of the St. Louis Cardinals, who filled a lawsuit against Twitter because someone tweeted in his name, using foul language and saying stuff he didn't like.
Just a little angry...
Maybe for Mexicans this is 'silly', but a for some people, companies and media in EU, his brand is very important and taking care of it in Internet is crucial.
A brand affected by a scandal or embarrassing situation must act fast or end up with a very bad image, like in those cases where people has reported objects or dirty stuff in fast food or the case of Domino's, when two employees put nasal mucus and saliva in sandwiches that they said were going to give to clients.
There are companies that by nature must take care of their credibility more than others, for instance, those who create news content (magazines, newspapers, TV stations, radio stations, news sites). If someone else uses their brand to misinformate, this could be a catastrophe in which users lost interest and trust in that company.
We have been seeing this kind of phenomena in Twitter lately, at least here in Mexico. At least a newspaper (La Jornada, which thanks to questions about his objetivity various users -including me- discovered that was a fake) had two fake accounts. Fortunately seems that Twitter suspended (at least temporarily) this accounts and both accounts lost all their followers.
I don't know why, but Mexican media isn't signing in to social media sites to protect their brands. It could be lack of human resources or just lack of interest in this kind of networks, but as users of this sites it's good to see Twitter is trying to do more in suspending fake accounts. As users, we will like to know that we are following the real thing and not accounts that use the name of a media company to tweet political stuff or try to influence people (particularly now that elections are close).
