Newspapers are famously printed on the lowest quality recycled paper and cheapest print process available, because they're disposable. Compare a retina screen to a coffee table style reference book with high resolution photos – the kinds you can use a magnifying glass on - and you'll still notice differences.

Or just look at what companies do when manufacturing technologies allow them to push for higher densities: iPhones now exceed 450 dpi, and the 8" iPads exceed 300; if the technology allowed it, Apple would most likely introduce higher densities on larger iPads and Macbooks as well.