Like other post-processed tilt shift effects, this will look best when objects are very short when measured perpendicular to the blur. If you have an object that spans most of the frame and crosses the blur then you will have parts of the shot which are at the same focal length but have different blurs which will give away the effect.

These examples were well chose to avoid this issue. The Empire State Building actually has the blur running vertically which is why you don't see it there. And the airplane is a great example because the front of the plane and the jetway are in a plane and the falloff was well chosen to start just above the top of the jetway.