Some of these are relatively difficult, but I just don't think any of those games come all that close to the skill gaps in the most difficult games. I haven't played all of the games you listed, of course, but God Hand took me a few weeks to beat on the hardest difficulty; I could probably have spent a couple more months, if I so chose, completely mastering it. The same is true of Ninja Gaiden.
Starcraft, on the other hand, is profoundly more complex, deep, and difficult to master. Men of War perhaps even more so. Generally, multiplayer games are where people looking for a challenge go (the other option would be score attack games, e.g. Tetris). In other words, I agree God Hand is considered difficult for a single player game, but single player games in general are going to present far less of a challenge than a skilled human opponent. Present day AI just isn't comparable to an intelligent human.
