This is what it comes down to when Israeli politicians urged that Hizbollah leader Hassan Nasrallah go to the head of the hit list. There are several reasons for this. The more obvious one is that Nasrallah is pretty much personally responsible for getting 1,200 Lebanese and 150 Israelis killed over the Summer. Many Lebanese would also love to see Nasrallah get lit up. But the Summer violence brought in all the diplomats and peacemakers for Nasrallah to play with, conferring some legitimacy on the warlord running south Lebanon. But there's a more pragmatic case for killing Nasrallah. Unlike many other terrorist organizations, Hizbollah doesn't really have a lot of depth. Nasrallah would be missed, especially if you were fond of a guy who might, at any time, make suicidal decisions. Nasrallah's decision to kidnap Israeli soldiers last July was a big error in judgment, and many Hizbollah leaders admitted it. Nasrallah will probably do something stupid again, unless he is replaced by one of less adventurous (and less capable) subordinates.
For the moment, the Israelis have taken Nasrallah off their hit list. Officially, anyway. If nothing else, this makes Nasrallah nervous and keeps him on the move.
Israel has found, in the past five years, that the best way to shut down attacks by terrorists is to go after middle management and technical staff. These are the people most responsible for making terrorist attacks actually happen. It's not the suicide bombers themselves, and it's not the top people in the terrorist organizations, it's the people in the middle. As a practical matter, there are too many potential suicide bombers to even try to go after that element. As for the top leadership, they are not as critical to the operations of the terrorist organization as was once thought. Moreover, if you nail the top guy, there are plenty of potential replacements. There's another problem with killing the top dog, as there tends to be a diplomatic back-blast when you whack the head of a prominent terrorist organization. These guys tend to have spent some time hob-knobbing with world leaders. Some respectability rubs off, and heads-of-state don't like seeing their peers getting assassinated.