If everything runs on one system in one location then yes your right. They don't and in that changes are propergated periodicaly. By saying it will take upto

If everything runs on one system in one location then yes your right. They don't and in that changes are propergated periodicaly. By saying it will take upto X days covers them on this front and in that protects there liability. Also note that they don't do them instantly to prevent forms of account denial of service attacks by having bots create and delete accounts instantly. But if you run your own mail server then you can just instantly add those email senders to your bounce list and get a much better effect.