The iPhone 6 is getting bigger. Simply doubling the pixels isn't as neat as before, there is no real reason to do this like there was before. Again, think of the iphone 4 as doubling the density rather than doubling the resolution (because the screen stayed the same size, it just happened that these went in hand). Do Apple want to increase the density on the iPhone 6? If they do, yes the simplest way is to double the density. That would be 326*2 = 652ppi. Over a bigger screen this is actually MORE pixels than doubling the existing pixels. They probably don't want to increase density though. They probably want to keep that the same. Thus if the screen is getting bigger, this means more pixels, proportional to the screen size change. The screen is not doubling, I don't see why they'd double the pixels.
The only reason they'd need to double the pixels is if they were going for a considerably higher PPI. What it looks like they're doing is going for the same pixel density, which means they only have to bump the resolution just enough to maintain 326 PPI on the larger screen. The end result will be just like it's showing in the photos on page 1, icons and widgets that are the same size as they are on the 5S, but with room to fit more in onscreen.