I don't buy that logic. How is it cross-platform? (It technically is, but c'mon. All of these OSs are in the walled garden.) I agree about RCS requiring Android, but that doesn't really put it lower than iMessage, since that also requires you to buy a device. (iMessage does have more features, though.) Apple has promised to support RCS in iPhones, so this should soon change. Also, why would iMessage be rated higher than Signal using this logic? What's easier, buying a device or installing an app on your existing device? (If someone doesn't have any mobile device, I don't think they really care about messaging anyway. So I don't consider that as a proper prerequisite.)