You must have seen a different Myth Busters than the rest of us.
I watched the same one you saw, but I was specifically looking for their results from the rifle to see if what they found agreed with Hatcher's testing. So it stood out when they never found any rifle bullets.
They did indeed recover bullets that had been fired vertically (out of a Garand). They did it out on a dry lake bed.
They did, indeed FIRE bullets from a Garand but they never recovered any of them. The only bullets recovered were from the pistol testing.
This was agonizing for them, for you could tell that they desperately wanted a different outcome.
It was agonizing because they knew that descending bullets can be fatal. They had documented instances of people being killed by descending bullets. So they knew that their results weren't telling the whole story.
Had they recovered some rifle bullets they would have likely duplicated Hatcher's results and gotten a result more consistent with what they knew to be true.
Here are the results from their website.
http://mythbustersresults.com/episode50
In the case of a bullet fired at a precisely vertical angle (something extremely difficult for a human being to duplicate), the bullet would tumble, lose its spin, and fall at a much slower speed due to terminal velocity and is therefore rendered less than lethal on impact. However, if a bullet is fired upward at a non-vertical angle (a far more probable possibility), it will maintain its spin and will reach a high enough speed to be lethal on impact. Because of this potentiality, firing a gun into the air is illegal in most states, and even in the states that it is legal, it is not recommended by the police. Also the MythBusters were able to identify two people who had been injured by falling bullets, one of them fatally injured. To date, this is the only myth to receive all three ratings at the same time.
Note that they say that the bullet will tumble. This was based exclusively on the recovered pistol bullets since no rifle bullets were recovered. Hatcher's testing conclusively proved that at least some rifle bullets will remain spin-stabilized and fall base first.
Note also that they specifically note that they are aware of descending bullet fatalities.