Whether this sort of situation has only recently become an issue, or else it simply hadn't been addressed before, you can't argue that gaming sites aren't pulling their weight when users don't behave the way they'd like.
With EA recently locking out a user due to their comment on a forum board, it seems more situations are coming to light.
A user of Steam recently violated their Subscriber Agreement, losing access to their nearly $2000-worth of games as a result. Why did this happen? The user wanted to sell their Steam account by posting the following on Reddit about a month ago, and Steam found out.
"Obviously I don't want someone to pay $1800 for my account. I'm looking at money of course, not full price considering I bought most of them on sale, but maybe we can come to some sort of deal. I'm also looking for WoW time too. Other "wants" would be PS3 games, maybe PSP games too. Of course if someone actually takes me up I'll be removing my credit card information from the account, along with my friends list. I'll also give you the login information for Global Agenda, Guild Wars GOTY, and any other needed login information."
About a week ago the user was informed that the account was in violation of the Agreement and, in turn, was disabled as a result, preventing the user from connecting to Steam. The user later claimed on another Reddit post that he or she was only curious to see "how much someone would pay for a profile like that", yet further stated "I WAS 'trying' to sell my Steam account", completely validating Steam's actions.
The Agreement does state "you may not sell or charge others for the right to use your account, or otherwise transfer your account", and with the user having a clear intention of selling their account, they had every right to disable it. Unfortunately, for this user, it looks as though the ban will be permanent, as you can decipher through this e-mail chain.
With any contract, whether hand-written or online, it is always a good idea to read the fine print before you decide on a particular course of action. You'd think it's common-sense, but usually that isn't the case. Had this user taken the time to make sure what they were doing was okay, their account would still be active and the $1,794.52 spent on their games would still be in their virtual console, instead of merely being a large dent in their savings they now have nothing to show for.