As far as the official Battlefield forums are concerned, they will give out a first offense warning. I personally received one for use of the word "christ's." While it certainly sucks for the people who have been banned, something tells me they probably went above and beyond in relation to vulgarity to earn themselves a ban. However, when you're in a forum for a game that has a single player campaign filled with obscenities, it's hard to wrap your head around exactly why EA would be so sensitive to such obscenities coming from their community.
Perhaps we should create a fictional account of a once feral child, who now at the age of 18, is socially adjusted enough to enjoy his/her first combat simulation. Prior to playing through the first three missions of the single player campaign, the now young adult had never used a vulgar word. But after just three missions, the young adult has discovered a whole new language in addition to the language he learned through his/her late Catholic upbringing. In other words, EA taught he/she how to cuss.