ORIGINAL: Straightarrow

There are lots of things that can make a difference. Some people center a pin, others center the site. High grip or low grip will cause variation. Peep to eye distance can vary quite a bit, which will cause some difference in POI. Almost everyone applies some torque to a bow, and almost everyone is a bit different in how they apply it. Even though with good shooters it's very small, the torque is still there. Another possibility is bow cant. If it's not the same, then POI will be off. Shooting different releases can cause some variation in how the string is released.

Add everything up and it can be quite a difference between two people. This is something I thought about quite a bit because there is a very good archer at the local shop who's POI is about a foot from mine at 20 yards, using the same bow with a peep. The good thing is it's always the same distance when shooting at 20 yards, which means were both repeating our shots with consistency.