Resolving the ambiguity of the ending is the entire point of this extended allusion. We have the sacrifice of a negative character (Batman) redeeming his positive aristocratic double (Wayne), and then general images of social redemption (even down to the visuals of children returning to the garden) as Gotham moves beyond the political/economic oppression that the film claims has thematically resulted from Batman's vigilante behavior and his refusal to trust in the norms of democratic society.
A great movie and widely misunderstood! And very suitable for the HN crowd given that it operates as an extended critique of the American war on terror. Some more thoughts for anyone curious:
Warners Exec: "Leave it open ended, Nolan, so we can make sequels, or you're never getting another dime from us."