Hmmm...not really sure I'm for it, but in defense of the OP's idea there sure are a number of overpriced guides out there for games...many of them not so great. I suppose this is similar just a different medium. Before the (public) Net and print guides, I remember making $1.99 a minute (or similar) calls to Sierra -- back in the day, for tips.
Collector's edition of EUIII had printed strategy guide and EU: Rome had .pdf strategy guide. I did read those and manuals once when games were first published, but many things have changed since writing and those aren't that useful anymore. CKII has no strategy guide and it's manual is considerably shorter (CKII manual is about 50 pager when Rome manual is about 100 pages and EUIII manual is about 150 pages.), but despite all that I feel that manual already explains the essential things which you need to know before you start playing. Only thing which I find often lacking with Paradox games is that they don't usually write proper manuals for expansions and you'll have to find everything yourself.
But for those who want to know how everything works (numbers and stuff) I recommend FAQ subforum. There's rather detailed stuff.