The attack, IMO, was meant to be symbolic to the Israelis. El Al is one of the hardest targets around, but this guy found a way to attack it, even if it was on the periphery.
You might be right since there was a second attack on a plane in flight reported in this morning's news.
But I think the Israeli's are well aware that no target is impenetrable. After all, they have such tight security in Israel, and still suicide bombings happen.