As Vadim said, it's about display of power.
However, I'm not worried about terrorists attacking infrastructure
under the cover of Presidential No-Fly Zones;
I'm more worried about backhoe drivers named Bubba
who didn't call the "Call Before You Dig" number
and weren't noticed by cable route overflights
because they were grounded while Bush gets his hair cut.
On the other hand, that's what diverse cable routes and
rapid restoration systems are for,
and even with air patrolling of cable routes,
there's the occasional Bubba who's checked with the
call-before-you-dig people (so the air patrols don't stop him)
and makes a mistake about where to dig...