Lance, just FYI, i do have "some" off-roading skills myself.
Yes, taking the correct line while off-roading is important...however, like everything, there is a limitation to that too if you're not in a capable vehicle.
For example, let's take a cross-axle situation (one front and one rear wheel is up in the air), which you see often in rock climbing. If you're driving an Isuzu Amigo (part-time 4wd with open diffs), then you will likely not make it across no matter what you do because you don't have a capable vehicle for that terrain (aka no ATRAC or locker). (And no bypasses are available.) In fact, you will probably break something from trying too hard. Now, you take the same situation in a 4runner...and you get a different result...you make it through.
So, is it really JUST 10%?? I don't believe it. IMO, this 90/10 rule was made by wannabe off-roaders who want people to think how good they are.

"Oh yeah, i climb that rock hill with my bare hands & skills...it's not the Rubicon that did it! It's all me!"
Why do seasoned off-roaders go out and buy the Jeep Rubicon?? Why would they modify their Jeeps?? Wouldn't they just be JUST AS GOOD in a regular stock Jeep?? Oh wait, to be technically correct, they should be 90% as good in a stock Jeep.
Jeff Gordon in a Yugo cannot beat me in my BMW M3 on a race track, even if i tailspin every 10 yards!

(Well, that is, if my BMW doesn't break down along the way!)
I agree 100% with you on one thing: KNOW YOUR VEHICLE. This is the most important thing IMO. Know your angles, know how your 4wd works (and it's limitations), know when to quit.