There was never a technical reason why we couldn't have this. Mostly Microsoft and Apple blocked this sort of generalization at every turn. And web standards fell to design-by-committee so there was never any hope of unifying these things.
Is it a conspiracy theory when we live under these unfortunate eventualities? I don't know, but I see it everywhere. Nearly every device in existence irks the engineer in me. Smartphones and tablets are just the ultimate expression of commodified proprietary consumerist thinking.