During the primetime broadcast of The Voice and the NBA playoffs Tuesday night, Apple unveiled a new, lengthy advert for the iPhone 5S, its high-end smartphone. Its a fun spot, featuring several musicians covering the opening to the popular 1988 song Gigantic by Pixies, while artists demonstrate the various artsy things you can do with the iPhone. But the song choice is rather interesting for a button-up company like Apple, given the songs sexually charged lyrics. Fans have speculated for years about whether or not the lyrics describe a couple having sex, with someone else watching. …