What Harlequin said. It's basically their "way" of advertising, using bigger communities like Aeria and Steam to draw players in.
I have mix feelings about Steam. Basically, you can't create a separate account once you log on with Steam. Meaning? You're stuck with the account linked to your Steam account. Though, Steam provides really nice exclusive items in their DLC section for RO2.
Whichever side you choose doesn't matter, as long as you enjoy the game.
Harlequin, you should come back!