It is a damn shame, yeah. But I think it's a consequence of the fact that every Holmes adaptation now feels a deep and abiding need to be serialized (why, God only knows; it certainly wasn't a characteristic of the original stories). And that demands certain things - it demands a villain (and to have anyone but Moriarty as the main villain would be strange, since there's so little serialization and no other villains who have the status of standing outside of a single case in the way Moriarty does) (even though he's only really in one case).

The Irene Adler thing is less comprehensible. I think it's because - you start out with a few things using her as an important character, and then she becomes a character that the general public is extremely familiar with, and it makes it easier to include her. You know, a bit of a reinforcing loop kind of thing.

I've always liked the Holmesian theory that Milverton was one of Moriarty's pawns, and that Holmes' defeat (such as it was) of Milverton was one of the things which led to the final clash between Holmes and Moriarty. And it does make me wonder why no one has taken that concept up, even in the context of a Moriarty storyline.

Or any of the other excellent Holmes stories that never really get adapted. Now I'm getting all worked up about this.