Look at the original article that started this thread. The courts mailed a copy of the order to an address the person never lived at then gave personal service to a "Jane Doe" saying it was his sister. He doesn't have a sister.
California got slammed under RICO for doing this over and over and over again. Many men never responded because the only notification they received was a garnishment on their paychecks.
Now, a guy who is served but doesn't bother to show up is one thing, someone who the state can not prove was ever served, that's totally different.
Look, the law gives you the right to go to court and say "I never lived there, I don't even have a sister."
The judgment can be voided but you have to actually get off your rear end and do something.
If you don't bother -- well, what is wrong with you?