all of the mentioned games can be installed and played without touching steam. And being mmo's they are updated as needed anyways. What do Steam bring to this?
Steam brings additional awareness to these games. The biggest problem these games have is a limited player base due to fewer people being aware of them. Also, Steam brings the Steam Wallet. This allows for you to have microtransactions handled by a single, relatively well trusted company, rather than having to trust your credit card info to multiple smaller ones.