1) Turf Wars is one of the major differentiators between Splatoon and other shooters. If we're concerned about how a general audience views it, I think "Fresh!" would be favourable, instead of "Oh so it's a King of the Hill game". If more people get interested at all, then they will discover Ranked on their own. They also avoid consumer confusion/disappointment due to not being able to immediately access the game-mode that they bought the game for [had they advertised Splat Zones].
Also, while you are right that it is easier for a newbie to join in on Turf Wars and not be completely useless, I think writing Turf Wars off as "Casual" isn't exactly fair. Just because it isn't ranked doesn't mean it can't be competitive.
2) Well the event is for more than just Splatoon, it'd be a bit weird to invite Splatoon specialists to a tournament based on general gaming ability.
PS. I really really want LAN play to get released, please Nintendo!