I've never cared for "The Mittani", his antics, or his alliance. This post isn't about him.
The CSM chairman, a representative of the 'hardcore' EVE player base, publicly advocated the harassment of player that professed to being suicidal. Whether or not the player was actually suicidal is not important. The chairman realized his mistake and wrote and apology, and that's also irrelevant.
The terms of the EULA are pretty clear when it comes to harassment and when the MOST visible player in EVE violates those rules, CCP has a few options:
a) Ignore the infraction and be accused of selective enforcement of the EULA. This option weakens CCP's authority to enforce their rules and makes the EULA a meaningless agreement.
b) Enforce the EULA without comment, as it would with any other player. The problem here is that the chairman is a very public figure and the incident was very widely publicized. A discreet response by CCP would do nothing to quell the controversy outside of the EVE community. Also, the EULA would be damaged because the perception would be that CCP does nothing to enforce the EULA (even if they actually did).
c) CCP makes a very strong statement in a very public way by enforcing the EULA with a disciplinary action even more severe than what would ordinarily be considered for such a violation. This preserves their moral authority, maintains the integrity of the EULA, and shows CCP's intolerance for that particular behavior.
d) The chairman resigns which saves himself the embarrassment of being the object of disciplinary action, saves CCP from having to make a tough decision, reinforces the EULA, and possibly earns him a bit of respect (and possibly loses respect from like minded members within his alliance).
Really, option A and option B are not realistic options for CCP. Option D is not something CCP can do (and might not be enough of a response if the typical response to this violation is to ban the account). Option C is really the only option CCP has. CCP has to defend its EULA and has to send a very strong message beyond EVE-O forums that harassment won't be tolerated.
Whether or not "The Mittani" had any malicious intent and whether or not the subject of his 'joke' took it serious, CCP has an image to maintain and and EULA to enforce. CCP wants to promote EVE's 'hardcore' image and has two products that will rely on this hardcore reputation to be successful. CCP has to draw a line with respect to acceptable behavior and be willing to enforce their EULA or else face the possibility that the next violation might be more widely publicized and more tragic.
EDIT: An anonomous poster pointed out that the EULA gives CCP discretion about how to deal with bad behavior and that the TOS absolves CCP of responsibility from players' bad behavior. (Sorta lke a legal 'dec shield' I suppose). No matter. I stand by my assertion. Bad publicity will force CCP to address the situation. Nice call, Anon. CCP apparently doesn't take responsibility for fostering bad behavior.