Nothing can stop a direct hit from lightning not even the best surge suppressors. As far as why the NICs took a hit? Krosus is right. The lightning hit was just trying to find the quickest route to ground and unfortunately found it though your NIC cabling to the NICs. I'm surprised the computers themselves didn't take more of a hit than they did. I've seen motherboards completely fry like that. One thing to look out for, though; just because it appears that the computers did not take a hit does not mean that they didn't. After a few weeks of use you may notice things like "Blue screens," GPFs and exception errors. This might indicate that the memory, processor(s) or motherboard did in fact take a mild to moderate hit. In cases such as this for me in the past, it became more cost effective to chalk it up as a total loss and completely replace the systems. It isn't worth the troubleshooting effort or the component replacement cost. Also note that with component replacement, that sometimes the new components you just bought fry due to over-voltages caused by other bad components. I guess when it comes down to it, electrons simply have minds of their own.
Also, I don't know if this is your case or not but most people surge protect the heck out of their computers but tend to forget to protect hubs, switches, routers, phone lines, ISDN, cable lines, and DSL ports which can all be points of entry.
Anyway. That was my two cents.
-J
