I am not saying whether it is true or not, but the logic th Discus guys follow is that to develop proper head and body shape you need to feed them like crazy on beef heart or other messy high protein diets, and obviously that makes frequent water changes necessary. I think the RO is a combination of the clean factor, and that it automatically makes for very soft water. I will note that the guys on the forum I have been following do have some very nice looking discus, with very good body shapes.
I suspect to some extent their daily water change suggestions are to keep noobs from making big mistakes. For example, I do weekly water changes, and recommend it, but if I miss a week my fish aren't going to keel over ( under normal circumstances) However, if you tell new fish keepers to do weekly water changes, many out of sheer laziness will decide bi weekly is fine, and a few will shrug and think because they only changed their water once a month with their guppies, that this is fine also.. Results, the bi weekly people will truck along, and if they have great filtration things will be ok, but som will have unexplained sickness issues, and some deaths, the monthly people will soon have serious problems and likely many deaths. So with the discus, maybe, just maybe those guys are trying to reduce the risk of a noob using a crappy filter and doing water changes every few days and losing all his high priced discus.
@Twisted sister, money is not the issue for me as it is for a school I teach at and they are paying for the fish, the tank and all. Got half of the tank together, but still waiting on them to order the important stuff like filters. After that the fish are not a problem since there is a local shop with extremely nice discus, if you missed it I posted pics recently.