> Given the nature of the Android ecosystem, I think we can be pretty sure that if it turns out that Apple bet right and the extra resolution is a good selling point, we’ll be in an amusing arms race around DPI PDQ.

Once you surpass the limits of human vision, where individual pixels can't be resolved at 12-24" distances (whether this is 300dpi or 400dpi, or whatever), there simply is no benefit to going higher. There are significant costs to increasing DPI, such as memory + GPU bandwidth. The hardware/manufacturing limitations are probably costly as well (does _anyone_ manufacture displays in volume with > 350 dpi?)