Maybe for those already using Steam. But for anyone else, it just adds another unnecessary step to accessing the game, one it isn't likely they'd take.
Exactly why I think Steam is a poor measure. Clearly there are many more people who login to MMOs directly than there are who access via Steam.
Do you understand when companies expand they look for other venues or platforms to help them succeed? With a pool of 7 million players it is not bad to reach out and see if their ideas sell to them. The download in Steam are relatively faster than most online source (I use it for that purpose as well).
Now let's just say you opened a new restaurant and deliver a new theme to add along with it. New theme, new restaurant you find yourself at the beginning of the launch with 100 customers right off the bat... and in a matter of 14 days you lost 40% of these customers. Do you think your main branch with the same exact theme is not affected at all?
One can safely assume with the huge decline in numbers on your newest restaurant represent the same overall health of your main branch. Hey but maybe the main branch caters to a in-sync, same mindset of people who are relatively in love with that restaurant? That is highly unlikely to happen, but who knows?
Trends are there because they can follow the flow on consumers. Same reason i can find why Turbine is creating a MOBA game.... one can assume that maybe they follow a trend that hits a huge proportion of players like DOTA 2
As this thread appears to be primarily about the merits of Steam or pretty much anything except what's in the title or OP, I'd say that about wraps it up.