One thing I rather like about traditional, sandboxy D&D is that it firmly believes in self-empowerment. Once you've rolled up a character his or her fate is essentially in your hands; it's up to you to make things happen. You're the master of your own destiny - unless of course the bad luck of the dice declare otherwise. In this sense it provides valuable life lessons to youngsters (especially the geeky and bookish youngsters who the game attracts) - take risks, have adventures, make something of your life; even if you fail, which is a distinct possibility because the universe is a random and uncaring place, that's more interesting than staying in your comfort zone. Whether or not people learn those lessons is debatable, but I think they are there.
Another interesting aspect of early D&D is that it throws into sharp focus what I believe to be the crux of the human condition, namely: Are we bound by our genes or can we transcend them? Of course, the PHB doesn't use words like "genes". What I'm referring to is the way the character generation process, performed the way God intended it (3d6 in order for stats), etches the character's strengths and weaknesses in stone; they are his or her DNA as surely as your individual genome determines how tall you are and what colour eyes you have. On the one hand, this is restrictive: a character with an INT of 6 can't become a mage, just like a person as bad at maths as me can't become a quantum physicist. But on the other hand, stats can never restrict player freedom once the game has begun: it is never possible for a DM to say to a player "You can't attempt task x because your y stat is too low." You can try anything. This is somewhat contradictory, but it is also very human, at a basic level; it is the paradox that faces all of us. Your nature moulds you, but your consciousness fights to transcend that mould.
These are the thoughts once has after a few beers down at the pub watching England get beaten by Brazil in a meaningless international friendly.