Truth be told, pirated movies are probably a bigger concern than terrorist plans. One's rich buddies are more concerned with protecting THEIR IP than with preventing terrorism which could happen to anyone - but statistically not at all likely to be them. Remember that customs was created to enforce taxes.
But how would CBP possibly be able to determine that a movie you have stored on your computer is pirated anyway? And think of the potential maximum payoff: A few dollars in taxes.
Compare this with physical contraband, where a person might be attempting to smuggle across the border something extremely valuable or highly illegal (for example, artifacts from a country that bans their exportation).
In other words, it just doesn't make sense to "digitally search" a person's computer, as any taxes collected would be minimal at best. And the fact that CBP so rarely does digital searches anyway (the court said what, 10 in one million?) tells us that they don't really think they're going to find valuable contraband that way.
No, it's pretty clear to me that "digital contraband" is NOT CBP's objective. It's just a gross power play, intended to intimidate journalists and other "unpopular" types whose words might undermine public support for the extremes the U.S. government has gone to in the name of the war on terrorism.
I'm going to be very interested in seeing how the votes fall when the ACLU lawsuit makes it to the SCOTUS. I'm guessing yet another 5-4 decision, with the conservatives falling lockstep behind the government and the liberals on the side of the ACLU. Another Kennedy tie-breaker, I fear.