For what it's worth, I think the only version of D&D that did not base alignment on actions, but rather based it on intent, was 2nd Edition. For the most part, D&D appears to promote character actions that are "larger than life" through creating archetype personality types, and basing alignment on action lends itself very well to that concept.
In my game, it's all about choices and actions. (I'm a big consequences kind of guy.) If you want to be considered a Good character by the world at large, you should act like one. I also do not require my PCs to follow alignment, as they have free choice to act as they wish. In my game, alignment becomes a "descriptor" of your actions, not a "restrictor" of them. Of course, if you can't act in accordance with alignments that are required for your character class, you might run into some problems when certain abilities stop acting correctly, or an atonement becomes required... that kind of thing.
Essentially, actions are the player's choice, and by their actions shall they be judged.
As you might be able to tell, I don't get a lot of Good characters in my game as they increase in levels, and when I do, they are truely Heroes in the heroic sense of the word. (If you haven't noticed yet, the more power a character gets, the less likely they feel compelled to follow the tenets of a Good alignment.)
With Regards,
Flynn