Well, I don't know anyone who really consider 3 shots groups to be a good judge of a rifles capabilities.
Think of it like this... Here is a 3 shot group from my .204:
That group measures less than 0.4 MOA.
Now, imagine if I shot another 3 shot group that was a mirror image of this one, two shots together, but the third shot low instead of high.
As a 3 shot group, it's still 0.4 MOA but if I'd shot the top and bottom shots in ONE group, it's be 0.8 MOA and there's no way of knowing, from 3 shots, if that's likely to happen.
The rifle is still easily under 1 MOA but a 3 shot group might literally
be telling you only 1/2 the story.
Problem is, it might not too. You just can't tell from 3 shots. Now, I've shot this particular rifle and load enough times under enough conditions to know that it shoots at or under 1/2 MOA "all day long". You'd really, really
have to screw something up to approach 1 MOA with this gun. I've shot it out to 410 yards and it shoots about 3/4 MOA out that far.
But from those 3 shots, you don't know if the center of the group is going to be between the bottom two (which would be bad) or if it's between the bottom two and the top one (which would be good).
So, yeah, you need more than 3 or even 5 shots to really call a group but, as to the point of the thread, a "1 MOA rifle all day long." is not spectacular at all. In fact, I'd consider it to be a requirement for most of my shooting. If I can't count on 1 MOA, I want a new gun.