To me, this is like a automotive executive saying "the engine doesn't matter, they're all the same anyway". The engine probably doesn't directly matter to most customers and they are mostly the same. However, it's lunacy to say that the heart of your product isn't important. If the engine has problems, your customers have problems. If the OS has problems, your customers have problems too.
Yeah, developer tools and APIs are very important, but they're only as good as the platform they target.
On top of that, the border between OS and libraries is fuzzy; OS providers will move it to get a competitive advantage. 3D graphics (historically, even 2D graphics), virtualisation, garbage collected runtimes, the list is endless.
The majority of available operating systems provide similar system interfaces. The same is not true for user experience, developer tools and APIs. His point is that these peripheral features will determine the success of operating systems.
Consumers are more concerned with the shape of a car than the engine that's inside.
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.
Yeah, developer tools and APIs are very important, but they're only as good as the platform they target.