Once you start looking at the tables and the descriptions of what they are supposed to be doing, you are going to start wondering how anyone figured those tables out using reverse engineering. Personally, I wouldn't be in the least surprised to learn that someone in GM with intimate knowledge of the programming is (or was) being consulted in the development of these products. Surely $$ was involved, I would wager.
Also, from what I have been heard, is that both EFIlive and HPTuners know of a lot of other tables in the programming that they have not provided general access to in their products. Apparently they will open up other tables if they can be convinced of the need, even for a single individual. But first I guess you have to KNOW such a table exists in order to ask for it.
BTW, I'm not sure what the HPTuners forum is like, as I've only browsed there superficially, but I do know that the EFIlive forum can be damned frustrating to use trying to find info. There are LOTS of threads that just end abruptly without the issues being asked about are answered. So you find yourself left hanging a LOT when trying to do some research on what particular tables do and the best way to do relatively minor things. And nearly all of the help guides and tutorials are woefully out of date.
All in all, trying to learn EFIlive was not a whole lot of fun. There were some people willing to help, but honestly it appeared that most people were holding their information close to their chest and would rather that you contract them for help (meaning $$) than to offer help for free on an open forum. I guess nearly everyone who gets familiar with this stuff gets the idea into their head to go into business. Lord knows I've seen a lot of names on various forums advertising tuning services that you don't have to dig too far back to find them asking newbie questions before they hung out their shingle saying "Now in business". And it is my personal belief that there are a hell of a lot of tuners out there that really don't know what they are doing if they have to go beyond merely a very superficial adjustment to the tune.