In my experience, no one thing does the whole trick. Each thing (camo, being still, scent management, playing the wind, calling, rattling, etc.) helps a little, and a good system that includes a few or several helpful things mixed with a little luck are worth the shot. Pictures like the one above are certainly nostalgic, but aren't exactly 100% applicable to today's sport. Sure, blood-letting may have worked a couple times, and it may even work on a couple things today. On those things, go for it, but for the rest of the ailments, I'll take modern medicine.
Camo, by itself, isn't going to help you kill a deer unless several other planets are lined up. If you killed a deer sans camo, and "not by the book," several things had to be the case for that to work. In that instance, there were enough things going for you that camo wasn't the necessary edge you needed. No, their vision isn't the same as a turkey's, but camo certainly isn't hurting your hunt. Even if all it does is boost your confidence a bit, that's worth it when the ole swamp donkey you're looking for comes by.
All that to say: obviously it's not what Bill Jordan wants you to think it is, but it's not necessarily pointless, either.