Can you direct me to the page that does this? I reached no such conclusion.
Another point to keep in mind is that every machinegun possessed by the military or your local SWAT team is part of the "common use" count, as far as I can see.
Just as it would not be reasonable to allow the government to cause an arm to become "uncommon" by prohibitions, similarly the government should not be able to cause an arm to become "uncommon" by monopolizing the functions which require the arm.
When the National Guard finally showed up at the Los Angeles riots, they were "commonly" armed with M16s, not the poor semi-automatic arms that the Korean storekeepers had been legally constrained to use.
When the SWAT team arrived at Columbine, they were armed with M16s, not the poor semi-automatic arms that a citizen attempting to rescue the students would have been legally constrained to use.
The increased manufacturing cost to create an M16 rather than a semi-automatic rifle of similar design is probably less than ONE DOLLAR. Every single AR-15 type semi-automatic rifle would be an M16 if not for the government prohibitions. If you don't want the M16 to fire in automatic, you just move the little selector to semi-automatic.
What did the National Guard do about the Korean storekeepers when they arrived?
Pages 44, 52, and 65.
And certainly, the difference between an AR-15 an an M-16 is less than a buck - the semi-auto version is a bit more expensive to produce, by a few pennies.
I have to think about your common use argument - while I like it, I am not sure that the court would buy it.