Pagers aren't deadly weapons. There's not going to be a huge amount of shrapnel, and the explosion isn't going to be at high velocity. Moreover, people don't necessarily carry pagers near their vital organs. So I'd expect a lot of injuries and few deaths, which is what was reported.
The virtue of this attack was disrupting Hezbollah communications; making the Hezbollah operatives afraid of infiltration; and sure injuring some fighters can't hurt but I don't think it was the point of the attack. I'm no military strategist, though.