Actually, that's 163 ppi for the first three iPhones, the two iPads are 132 ppi, and the iPhone 4 and iPhone 4S is 326 PPI (as correctly stated, double 163 ppi).
No problem, the 2 and 3 dpi difference is not noticeable. But when doing the math, it was getting all screwed up. Doubling the linear numbers just weren't matching. And the number of pixels and ratios were messing up too.
130 dpi for the iPad would cause confusion because that would mean a 9.85" display, then one could wonder if that's 9.9" viewable and 10" display, etc.? The iPad is a 9.7" display.
Same with the iPhone, it's very much a 3.5" display. the 160 doubled is 320, but it's actually 326, just wasn't working! Again, not noticeable, but the other numbers would just cause confusion!