I read about the decision, but have not actually read the official version. However, if what skeet_man says is correct, (and there is no reason to doubt him)the reasoning of the dissent is curious.
The 2nd Amendment was originally passed as a FEDERAL law, and is one of only two amendments not specifically "incorporated" into the Constitution (by the US Supreme Court) as being applicable to the states. (The other is the 3rd Amendment regarding the housing of military personnel in private homes.)
The incorporation argument is something like this: if the amendment is NOT incorporated into the consitution, it applies ONLY to the FEDERAL government, not to the states. Thus, carrying that premiss further, if your state does not have a specific STATE Constitutional right to bear arms, you don't have one. I don't necessarily endorse that logic, but it is possibly true... you never know how a court may rule (unless they are "liberal" then you know gun owners lose).
Now, since DC is NOT a state, it is subject ONLY to FEDERAL law... there ARE NO state laws there. Thus, the dissent's argument is logical ONLY if the dissenting Justice is a LIBERAL, and the decision is made from a POLITICAL, not LEGAL perspective.
As someone pointed out we don't know who will be President in 2 years. Hopefully, someone will appeal this to the Supremes. If they accept cert, we'll at least get a ruling, and hopefully it will be favorable. If they do not accept cert, at least the DC ruling will stand for the DC circuit, and might influence a few other circuits to rule similarly... except of course for California. Those guys are probably screwed without a Supreme Court ruling.
Perhaps the reason no gun case has gone to the Supreme Court since Miller in 1938 is that ever since Roosevelt packed the court in the 1930's, the court has been leaning left until now.