GUIs go to great lengths to work around the low ppi, using anti-aliasing, (auto) hinting, subpixel rendering and various other techniques. This kind of thing g

GUIs go to great lengths to work around the low ppi, using anti-aliasing, (auto) hinting, subpixel rendering and various other techniques. This kind of thing generally isn't available for bitmaps such as the comics in the Humble eBook Bundle which are consequently extremely difficult to read (the images are a higher dpi than the screen so it is a screen problem not a source problem). You are right that there are people for whom extra ppi, extra cpu, extra memory, extra power saving, better colour gamuts etc won't make a difference. But there are also a group who do want ppi improvements and Apple has done so across their laptop and tablet lines, Asus has done for some of its tablets, and the Nexus 10 has done so too. If nobody bought those then it would demonstrate lack of demand, but people have been buying them. And people really want them for non-Apple laptops too as Linus stated and others have concurred.