I quite recently noticed a trivial detail but which I'd like to share with you. The book is thin even for an AD&D book. Compare it to any latter edition and it's only 130 pages long versus 256 pages on the 2nd edition and similar number in the 3rd and 4th editions. If you don't count the list of spells, which I believe are not compulsory reading (even though it doesn't hurt to skim the spells especially if you're a class that can cast spells), and the apprendix that contain mostly optional rules (psionic powers, the bard class, and so on), each player only has to read 40 pages of stuff. This is on par with most of the so-called lite rules systems. Even the Moldvay edition of D&D is almost equivalent in the number of pages. Notice that I'm not comparing rules complexity, only rules quantity.
This is mostly due to the fact that the majority of rules one considers important to players, such as combat, attack charts, etc. are relegated to the DMG pages. Let's not forget that it was explicitly stated that none of the players could ever, ever touch the DMG on pain of being obliterated by a blue bolt from the sky (not quite the same words, but the intent of the DMG foreword is the same). I believe this may actually help the players be more creative and flexible in their decisions when facing the situations the DM throws at them. The only rules the characters ever need to know are actually in the PHB: what each races is, what each class does in terms of special abilities, equipment lists (minus encumbrance which is, you guessed it, in the DMG), and some very nice suggestions about how to go exploring dungeons.
I don't pretend to know the editorial decisions behind this. Perhaps someone can shed some light. However, no one can complain about reading a whole lot of rules just to play the get. It remains highly accessible from a player-point of view. Certainly more accessible than latter editions. What I firmly believe is that it frees the players to approach the game creatively instead of a more simulationist mindset. With no rules to memorize, the players can describe their actions freely, which the DM must adjudicate using the DMG as guideline. No more "what maneuvers do I need to know" or "wait while I check this and that to see if it's a viable action". It's comparable to a computer game where the player just decides his actions and the computer does the rest. The downside is that the DM is burdened with a lot more rules than players are accustomed to, but then again most players don't read the rules anyway.