The system is only designed to intercept missiles on course to strike built-up areas. It has therefore had a much higher success rate than you present. It is also worth noting, the time the system has to respond, with regards to missiles fired from Gaza, is extremely tight - this will not be the case with incoming missiles from Iran where such defence systems will have significantly more time to respond. Both Iran and Hezbollah will be extremely concerned as it provides Israel with an additional level of defence of it's most sensitive areas.
Kerry: Pollard's parole not related to Iran deal (Reuters)
from the article: A look at Israel's 'Iron Dome' missile defense