What this speaks to is making a contract void. The TOS is a binding contract, that does not make every clause in it valid. If a online game company made a game that expressly promised online play and never delivered online play, the customers could very well sue them and win regardless if they signed a TOS stating they would not sue. A lot of contracts have a forfeiture of right to sue most of which are invalid, this does not make the contract void, which means that everything else signed is still a valid contract just the invalid portion is ignored. A void contract nullifies the entire transaction and only arises when something unconscionable is contracted.
Three problems here:
1) Most people did get a chance to play
2) ToS specifically waives your right if the service is down, and you are expected to have read that agreement
3) There is no forfeiture clause in the ToS