Risking revealing my fascination with cheesy pop...
i hate to jump into this, but...
They used some extreme settings on the Antares AutoTune plugin:
i heard it was a digitech harmonizer..
http://www.antares-systems.com/products/auto-tune3.html
The plugin is found in any commercial studio and has been used for years to fix the vocals of our favorite pop stars.
Most knock-offs use it too.
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