Re:Yeah, only SPAM, sure. (Score 1)

couldn't Verisign work round this, by delegating x.com (where x is any unregistered domain) to a different nameserver (of their own), which would then return A records pointing to their advert server?

They would have to do this for every unregistered domain, which would be impractical. The problem with the wildcard is that it catches all unreg domains under the given TLD by default.