I think most Amber fans still use pretty much the rules as written.
I think that there are two basic styles of RPG rules:
1. Systems which are designed to be flexible and house-ruled.
2. Systems which are designed to be firm and unbending.
Many of the early RPG systems, such as brown book
OD&D,
Tunnels & Trolls, and the like, seem to fit more into the first category. The designers had the idea that the rules create a structure and the GM can and should change them as they see fit to make the game work for them. They tend to be rules-light and are low on details of bookkeeping.
Other RPG systems such as
d20 appear to be more rules-driven and rules-heavy. The letter of the rule often seems to be more important than the spirit of the rule, and bookkeeping and "working the system" becomes more significant. (I don't mean to imply that this is a bad thing, but it is a different style of rules design.) The GM is encouraged to "play by the rules" and standardization of the rules is important.
I believe that ADRP was designed in the spirit of #1 above. As such, I would guess that most campaigns are run along rules consistent with most of the rulebook, but that most campaigns also have house-rule tweaks and modifications to fit the style of play of the game group. Loot at the number of ADRP campaign web pages out there and find a large number of variants of the same basic rules system: sometimes a tweak in which attributes, how many attributes, which powers, partial powers, new powers, canon NPC elders, and so on.
So ... I agree with the spirit of what you have said, that the game they play is still essentially that outlined in the rulebook, but I might disagree somewhat because of the house-rule natue of the game.
Am I just nit-picking? I don't mean to... :cool: