I agree, Lat pull-downs are more isolated, and they definitely have their place in every bodybuilder's program, heck even I do them. But in my experience, and from what I have read online, including many comments on Fitocracy, one thing people sortoff agree on, they are not that helpful to those that really want to learn to be able to do pull-ups. Many do agree on negatives, and my personal experience is, pendlay rows helped built me real strength I needed.
Will check out sixpacshortcuts, I actually need to find some good core ab exercises, I realized the other day, I may be lacking ab strength, my lower back curve way too much inward to my liking, and I want to even it out.