To pick up from where I left off yesterday and hopefully to address ziggi's comment at the same time:
What distinguishes the Patriarch's from others in their time and in later generations was their ability to communicate with God, to seek out a direct relationship with God and ultimately to secure a covenant with God.
Even though the way we see the story in the Torah, God first seeks out Avraham, the way the sages understand it, Avraham first seeks out God when he realizes that the notion of idol worship doesn't make sense.
Later on, there is an implication, which the sages pick up on and amplify, that Avraham kept all of the Torah including rabbinic enactments, even though he was not commanded to do so.
So Avraham's relationship to the Torah is an organic one; that is, he comes to keep the Torah as he came to worship God, by way of his own initiative and highly perceptive abilities.
This approach reflects a very high spiritual and intellectual level. While it is incredibly admirable, this is not a model that everyone else can emulate. We are not all blessed with those sorts of abilities and, perhaps more to the point, we are not all imbued with the spirit of seeking that Avraham and the other Patriarchs had.
Moshe, by contrast, is clearly sought out by God, even chased and sort of hounded by God. Moshe displays a different sort of critical mind and way of thinking. When confronted by God, Moshe steps back and says maybe I don't want this relationship. He challenges it on every level.
Moshe represents the person who does not figure out the Torah by himself; in fact, he represents the kind of person who challenges each aspect of the Torah as it is presented to him. Whereas Avraham was in harmony with the Torah and how it works in the world in some kind of intuitive way, Moshe needed to understand each aspect of the Torah as it came to him. Thus, I would argue that Moshe is the more appropriate party to bring the Torah into the world. He leads the way for the rest of us who need to understand the Torah in our own way and may not be up to tuning into the Torah on some kind of higher plane.