Customers do care about the engine, just not explicitly. They may want a car that goes fast, gets good gas milage, and is reliable. They won't ask about the engine, but it has an effect on those things.
By that same token, customers want a mobile phone that is fast, gets good battery life, and is reliable. Again, they won't ask about the OS, but it has an effect on those things. Thus, customers care about the OS; they just don't know it. Plus, I shouldn't have to tell you that similar interface != the same thing.
Consumers are more concerned with the shape of a car than the engine that's inside.