I mentioned heavier stuff because the author seems to specialize in metal. That being said, I think there's stuff for every one in there, as some of the basics remain the same, obviously.
But, unlike some other books dealing w/ somewhat more generic aspects of recording and mixing, a book written by someone who works primarily in a genre where everything is a bit more extreme tends to go into finer details, like eq techniques which may seem abusive in other genres or using a multiband compressor on guitars and such.
The funny thing is that, while there's tons of tutorials on mixing drums available everywhere on the web, the information on mixing heavy guitars is a lot harder to find (except here when Danny chimes in). And speaking even w/ experienced engineer, I've come to realize that it was often a pretty tough part to deal w/.
I've downloaded all available formats, thinking that at worst I'd put up w/ PDF - which I really don't like - but the first one I clicked opened in my Kindle application on the MacBook. That's as good as it gets for me. :)
I'll check out that review you wrote. I dug that book by Senior.