You have to take the author of this document into consideration. BMW is not going to go out and create a document informing the world that the N55 is not as good of an engine as the N54. So ofcourse its going to be filled with little info here and there showing the benefits of parts. Like weight savings. . But some of those weight savings weakens those part of the engine.
I have an N55 and had 3 N54's. The N54 is a stronger engine and has more durable internals, that is a well known fact.