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No it became UU because it was used a lot in UU. A Pokemon could have 50% usage in NU and it wouldn't move to UU unless it got a lot of usage there too.
Also Qwilfish is rather popular in a rain dance team.
First of all Zapdos isn't in NU and if it was it would probably be banned pretty qiockly. I don't think a single Pokemon could stop Zapdos since it would power its way through the entire tier, at best they could stall/wall him, but can't do anything in return.
What's you opinion of him? If a popularity contest came up what Pokemon would you vote over him. I'm asking this because GameFAQs is having their traditional contest and some people think he's popular because Pokemon RBY is popular on the site while others call him an avatar that the player...
I think the plan is to split NU into two tiers, but that is still a long ways away and if there isn't enough popularity it may not even get off the ground.
That's because those OU are stale. Last month before the change Alakazam and Rhyperior had 3.17 and 2.77 usage respectively while this month they took a drop. Look at past OU, Yanmega, Donphan and Dugtrio are no where near where they use to be when they were OU.
There's also the "Title" factor going on. Everytime a pokemon moves from UU to OU it gets a boost in usage while a pokemon takes a drop in usage should it lose the OU title.