While it's true that digg can do anything they want on their site, pragmatically speaking their development process may not support creating and deploying the change you're thinking of in a matter of minutes or hours.
An alternate explanation is that the bogus accounts are external, and digg blacklisted the IP's associated with those accounts upon learning of this. Most larger websites will have a fast way to blacklist IPs on their load balancers or the like simply to avoid buggy robots, spammers and trivial DoS attacks.
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While it's true that digg can do anything they want on their site, pragmatically speaking their development process may not support creating and deploying the change you're thinking of in a matter of minutes or hours.
An alternate explanation is that the bogus accounts are external, and digg blacklisted the IP's associated with those accounts upon learning of this. Most larger websites will have a fast way to blacklist IPs on their load balancers or the like simply to avoid buggy robots, spammers and trivial DoS attacks.
Or they froze the accounts by changing the passwords (and maybe the email addresses, to prevent password recovery).