You are right that the components used in phones/tablets could (will) become cheaper due to scale. But the effect will be the same as when laptops drove 3.5" dr

You are right that the components used in phones/tablets could (will) become cheaper due to scale. But the effect will be the same as when laptops drove 3.5" drives - desktops started using those components. It's the same as when workstations were displaced by PCs (and Sun died): PCs are now used as workstations (also, used as minicomputers, servers, mainframes). The usage won't disappear, because keyboards and desks remain useful. Soon, "desktops" will be displayed by devices that look like phones, but are used like desktops. Some will double as phones; some will be dedicated (like Apple TV); some will be desktops, like those USB computers. It's already begun. As a comparison, by one benchmark, the iPhone 5 is 3x as powerful of the first eeePC 701 - which I use as a desktop, with HD screen, full keyboard and mouse.