Question: It seems pretty normal to see screenshots of MS Word, steps for "this is how you generate a template". I don't think Microsoft would object.

But I'm not sure about reprinting images from in-game scenes for specific games, like Diablo II. Do you need to obtain permission to include a screenshot of a game in your book?

Answer: 
Depends highly on the use.

If you were for example to make a story book and just use diablo screenshots as illustrations, that would (probably) not be considered fair use even if it is transformative. Neither would it be if you would just publish an outright art book by using the game assets as they are.

If you were making a book about the history of gaming in general, you do not need permissions to use screenshots. For this there is plenty of precedent and it is generally accepted practice, much the same that if you're making a documentary about 80's action movies you don't need permission to show the terminator 2 poster in context in the documentary.

However, it would be better for you if you took the screenshots yourself as that can put in another entity into the copyright chain. In other words you can't just copy the screenshots from a book containing all the nintendo games ever published and put them in your book about all the nintendo and sega games published.

Even including long stretches of video from a game even in a highly critical piece just badmouthing the game for 15 minutes is fair use(jim sterling vs. digital homicide, although that lawsuit wasn't just about the video I think they tried to claim copyright over it as well along the way).
The copyright information included with the game itself should tell you the answer to this. They will set out the parameters of what you can and can't do.

My hunch would be that a specific screenshot of a game in action, created by yourself, would be considered 'an original creative work' and would therefore not be restricted by the game publishers copyright rules.

However, you would really need to consult a lawyer specialising in copyright to know what you can and cannot do legally.