Technically speaking it's just because Ford considered them two different engines.
The '72 with the dual points and 4 bolt mains is considered a "performance" engine whereas the the '71 (actually a '70 4v production engine) is not.
They are almost the same engine so it's just a rebranding by Ford and Ford trying to compensate for the lack of compression by giving the customer "performance potential" in the 4 bolt version.
I think they all run better with the 16 degrees initial but that's just my opinion. I'm sure that others will disagree.