Contrary to our myths (mostly developed by Colt in 1800's) most colonists didn't have guns.
There simply weren't that many around and "our" Army needed all they could get. So, hit the people up for them (what few they had anyway).
AFA "subject to reversal", interestingly Miller has been cited at least twice in subsequent USSC cases as precedent for further restrictions on firearm ownership (the ban against felons carrying them and the assault rifle ban). Hardly sounds like reversal is in the picture - they passed on at least two opportunities already - with largely Reagan/Bush appointees at that!
But take heart, Yendor, we do have a right to private firearm ownership. That is because the Bill of Rights is not an exhaustive list. Since private ownership of firearms having nothing to do with a State's militia is not contemplated by the Constitution, we have a right to private firearm ownership for as long as the Congress does not pass legislation prohibiting it.