A couple random thoughts.
What George notes above about foil is right on point. However, technology has changed on the foil front. Check out:
http://www.swagedies.com/mm5/merchan...ry_Code=HTREAT
I've used it to make some custom chisels and irons and it is great stuff. No need for foil, sacrificial carbon or anything of the like. Just heat the part slightly, shake on some of this stuff so the part it covered, let cool and put in the oven to heat soak.
Second, there is no need to go to all these lengths with your iron. Even an edge made with 220 grit sandpaper will stay sharp if the steel is hard enough. LN is not selling plane kits, he is selling top dollar planes that are supposed to work out of the box. The ultimate way to determine if your iron is too soft is to measure it. Look very closely at your plane iron. Is there a tiny dot that looks like a punch mark on the iron near the cutting edge? Could be on the front or the back. It will look like a tiny dimple, if there isn't one, it means your iron likely wasn't tested for hardness and could be faulty. If there is one, then it could still be faulty if the machine was not set up and ready properly,
I have a Wilson Hardness tester and will gladly test one of your irons if you want to ship it to me and put a return postage paid label in the box. Hardness is the ultimate proxy for quality. If your iron tests at 40 on the C Scale, it's never going to get hard enough to hold an edge. Could have been all the carbon migrated out like George noted, or more likely could have been improperly tempered and most of the hardness has been removed. Only way to know is to test.