A poor player hopes his opponent will overlook something.
Excellant analogy. Here is my thought on their analysis and strategy.
They obtained a stay of the DC Circuit mandate which covered everything including safe storage. They appealled only that portion dealing with the handgun ban. They anticipated an argument from Heller in respondents brief asserting that the availability of rifles and shotguns for self defense was illusary due to the safe storage laws. They would then respond that Heller is whacko since the DC Circuit found that to be unconstitutional and the District did not appeal same, therefore Heller's argument is without merit.
It would give them an advantage of possibly prevailing upon one of their alternate theories that they did assert to the DC Circuit without being burdened by the flaw in that theory pointed out by Heller.
Of course they hope to prevail upon a theory which will allow them to reinstate the safe storage laws, but this tactic was a backstop that they perceived to be without any risk. If they win on one of their other theories they did not lose a thing. If they lose to Heller, they would have lost the safe storage anyway...
What they did not anticipate was Heller going back to the DC Circuit and asking the DC Circuit to modify the stay of mandate. I am sure there are more than a few 3 piece suit types that are a bit redfaced right now, scrambeling to shore up the devastation caused by Heller's motion.
Hellers motion accomplishes more than merely providing for a modification of the stay. It provides Heller with ammo to use in his brief to show that the District really intends to enforce the safe storage laws and diffuses totally the trap that the District had plotted out.