It's not as if those opposed to Iran's nukes avoid such drastic action. Two top Iranian nuclear scientists were murdered under suspicious circumstances during 2009 and 2010 and a third was critically wounded.
Iranian officials charge was developed and released by Western powers, probably Israel and the U.S. Israeli officials have acknowledged testing Stuxnet after it was found in the wild, but have been cagey about what other involvement Israel might have had.
Terrorists attacking SCADA systems in the U.S. could potentially hinder or destroy automated industrial systems in hydroelectric dams, oil-refining facilities, water-processing facilities, traffic systems and other systems that make the real world work.
Hacking banks or the cell phones of celebrities may be sexier exploits because they make the hackers rich or famous. If they're serious about attacking the U.S. and making a real impact – killing people, damaging the economy or civil infrastructure, SCADA systems are the way to go.
Today's news just confirms what security experts thought – that SCADA systems running U.S. industrial facilities are vulnerable, and so are the people who rely on them.