Precisely this is what I do. I haven't had a domain banned since I started deleting the entire campaign from my account before setting up new account to run same domain. I think what happens, and this is just my wild assumption, not saying it is facts, but I think the only system Google has in place is, "CHECK to see if this domain is being used in account", I imagine they press a button, and a robot goes out and crawls every account in 6.2 seconds. Wait a minute this is Google I'm talking about. I imagine this check happens in 1.7 seconds. Most people when they have abandon an account never think to delete the entire campaign, so I imagine when Google does this imaginary check, that I imagine happens, it shows they are already in the system, it links them to a previous account. Most likely delinquent, they get ban Hammer!