Why would they have to hire a 100,000 new workers? Wouldn't the existing workers on the iPhone 5 and 5s lines be sufficient to cover production moving to iPhone 6? Or is Apple counting on a mega explosion of sales in a somewhat saturated market (in the West)?
Probably because it's a ramp up to build stock up for launch. A large part of those 100,00 will lose their jobs after the initial ramp up just like the 100,000 extra likely lost them after the 5 and 5s initial ramp ups. Big difference between being ready for a surge in last quarter if the year, and "steady state" production.