In Sunday's New York Times, Matt Richtel explores the arbitrary intricacies of the Transportation Security Administration's rules concerning electronic devices carried by air travelers:
A spokesman said the agency has its reasons for still requiring that traditional laptops [but not, say, tablet computers, e-readers, or smartphones] go through X-ray machines in a separate bin. But he declined to share them, saying the agency didn’t want to betray any secrets.
As I did more reporting, the logic behind the rule grew as elusive as a free power outlet in the boarding area.
Richtel notes that there does not seem to be any security-relevant characteristic, including size and interior capacity, that consistently distinguishes laptops, which have to be removed, from electronic equipment that you're allowed to keep in your bag. The TSA's blog at one point suggested that laptops with relatively small screens (11 inches or less) can stay put, but Richtel was unable to get an official confirmation of that rule. He reports that a security agent at the San Francisco International Airport, which hires a private contractor to to do its passenger screening, told him iPads need not come out while warning that "other airports might be different."
As usual, the most plausible explanation for the TSA's policy comes from people outside the TSA. "Is it thicker than an inch, wider than a piece of paper, bluer than the sky?" says security expert Bruce Schneier. "Who cares? It's all nonsense." Robert Mann, an airline industry analyst, tells Richtel, "It's a difference without a distinction, at least from a security standpoint." An unnamed security expert says (in Richtel's paraphrase) "the laptop rule is about appearances, giving people a sense that something is being done to protect them." He calls it "security theater" (a term coined by Schneier).
I would add a corollary to the rule that TSA policies are mainly about appearances: As with other bureaucracies, the stupidity of the policies is compounded by the ignorance of the agency's employees, who often do not know what the policies are.