The autospam filters are based on googles own findings, updated every 7 days. Or were..
so basically they monitor some number of honeypot sites, whatever spam turns up gets add to the autospamban list used for everybody.
So if the spammer/s do not match any of their patterns etc, then not in their list, not banned.
No doubt it helps - but if you have a very specific set of spammers, not gonna help much, as they won't be hitting any of the honeypots
It gets more confusing telling the difference between blogspot and blogger, so not sure they will have the same features? even though both are google powered.