Because I think both cases involve a bureaucrat's favorite piece of legislation--the Administrative Procedure Act.
As I understand it, Obama is being sued by Texas because he didn't follow the public rulemaking provisions of the Act. Texas argues that the state is harmed by Obama's actions, meaning that he (ICE actually) should have gone through proposed rulemaking, allowing the public to comment on the actions. There's a prediction the court fight may drag out through the rest of Obama's term in office. (If they had gone with proposed rulemaking, the administration's lawyers probably figured it would have taken a couple years to complete anyway.)
If the FAA actually gets their registration system, both software and system design and requirements, up and running by Christmas, in time to catch all the drones being given for Christmas, they will have done well. But why aren't they required to go proposed rulemaking under APA?
My guess is the FAA's argument in fact, if not formally, is that no one will have the balls nor the legal basis for suing over APA procedure. They might say that the registration system will be so easy and not burdensome that there's no adverse burden to the public. What I suspect they'll really mean is that the drone industry wants certainty so they can forge ahead, so no company will sue. The industry will do better by having known standards than a 2-year court fight over process.
Now from the private citizen's standpoint, I could argue that my freedom is impaired by any federal regulation of
I could argue that, but I don't. I wish the FAA good luck with their software project.