Going off from this post and adding a poll: http://www.gamesas.com/topic/1490799-steam/ (dead thread)
Do you think it is beneficial for the game to be released on steam? It's funny when I saw http://www.vgchartz.com/game/70799/the-elder-scrolls-online/ on ESO and thought of reviving this topic.
For me, it's better for them to give a go on steam after the game's release. If the outcome of the game is positive in its first months release, then it would garner good publicity during steam release. I've actually gave someone a beta key in steam and said in reply that he was not interested in an MMO, and was hearing bad things about the game. If the game's release would prove otherwise, then it will possibly pull these people into thinking of buying.
And, think about the cut steam will get when the game is released over there. In a corporation's view point, it's better to milk people first with the most return.
For people who are against steam platform due to connectivity issues, there are games/MMORPG that you can run without even launching steam such as Path of Exile, but you can still connect with people who launched that game via steam.