After thought, there seems to be a connection between the anniversary of creation and judgment. הַיּוֹם הֲרַת עוֹלָם, הַיּוֹם יַעֲמִיד בַּמִּשְׁפָּט. Perhaps an analogy can be drawn to the melech basar v'dam, Paaroh, who celebrated his birthday by calling the convicts from their jail cells to determine a final judgment. Kings use auspicious occasions to demonstrate their kingship. Perhaps that is so with the King of Kings as well.
Thoughts?