I had a lively debate about this last night via google hangout with a few friends. It was posed that our effort to recast Arduin in its more original format meant it would join the ranks of OSRIC, Labyrinth Lords, and others. My protest to that idea was that Arduin was not a recreation of 0E or 1E DnD but a full game in its own right.
That lead to a lot of back and forth as to whether Arduin ever stood alone as a singular game. While I conceded that in its original state, as discussed in AG I - III, it did indeed depend on the game material out there, Arduin had morphed into a game on its own by AG III.
In the end, the game changer in my eyes was the Arduin Adventure. That volume, Arduin truly stepped forth as an independent game without ties. While I had some dissenters, the vote swayed my way with the caveat that up until that point, it hadn't.
I'll agree, at least in the context of the printed material. Having availed myself to the trove of info DH left behind, it was obvious he made the switch well before he published the Arduin Adventure.
Additionally, Arduin played differently than 0E or 1E. Not to the point of dissonance, just more like cousins than siblings. Concepts of game balance went sailing out the window. Just a gander at Arduin's magic list showed that, further revealed by its artifacts. -10 AC? hah! I can remember scaling into the ridiculous extremes, taking on 10, 20 or more to that number. The same for other notions like level limits or a max to the number of magic items one could have and use on one's person.
Lethality? Oh yeah! I can remember numerous pick up games in my youth where a requirement to be at least 4th level was needed just to even think of playing in Arduin. That was with folks predominately DnD who had little experience in Arduin. They rarely survived a single session since not employing thought, tactics, and tried and true adventure strategies meant a short lifetime.
Now don't get me wrong. I'm not positing that the retroclones don't have lethality, fast, fun in-your-face awesome game play. They do. What I am saying is that Arduin came out shortly on the heels of the system that the retroclones are based on. It was a cousin and Arduin Bloody Arduin seeks to return to those good old days, just like OSRIC and Swords & Wizardry did by going back to the original DnD.