It doesn't matter if designing an API is hard... at least not in the US, which does not follow the sweat of the brow doctrine.
It does matter if API design involves substantial creativity. If the API design is not simple and obvious, and if the work to design the API is a substantially creative endeavor, the API becomes eligible for copyright, and indeed, this is what the courts have now found (at least in the specific case of the Java APIs).
As much as I don't like the idea of copyrightable APIs, I can't really fault the ruling.
Fortunately, the court has now also ruled that using APIs is fair use, which is an essential ruling from an interoperability PoV. And despite this op-ed piece, I'm certain that most companies will be relieved that there are limits to Oracle's absurd attempts to squeeze money of out any company that use Java.
Personally, I'm just happy that the company I work for chose C#/.NET as the scripting platform for customers, not Java. It was touch-and-go there for a while, but Microsoft and .NET has turned out to be much more trustworthy platform stewards than Sun/Oracle and Java.