If you can reliably farm A2, you can beat the whole game. Slowly but surely. You have to remember, game ended in Hell back in D2. It didn't take much to beat hell there and it doesn't take much to beat hell in D3. Inferno is just a bonus difficulty for masochists. It's equivalent to farming 13 Windforces in D2.
You can say that Inferno should then be easier, or good loot should drop more often (and I'll agree with you!), but then you should be ready to get bored, because there is absolutely nothing else to do in this game but wait for PvP, should our wishes be granted.