Oh god, DCOM memories. I've spent days in a futile attempt to get that working. The best demo of how bad DCOM is would be the existence of OPC Tunneler:
DCOM is such a headache that these guys sell a $1000 program whose sole purpose is to make it easy to make remote DCOM connections. And I've recommended it as a screaming deal at that price. Given what it costs to get myself or a proper tech to a remote site for a day, I'd much rather use that and spend my time solving the actual problem than spend a day trying to get DCOM working before working on the actual problem.
And afaik they didn't have internet access directly for the control boxes at Natanz. Stuxnet got into the plant via USB sticks.
[1] http://en.wikipedia.org/wiki/OLE_for_process_control