If they force the anti-spam nets to keep getting bigger and more sensitive, more non-spam will get caught in it. The spam filters become less effective, and used less.
You would think. However I do this every day, admin an anti spam solution global for 20K users, not send spam (among other things).
We look at the quarantines and the scoring of all pieces of an e-mail. We then adjust our custom rules to become more effective while keeping in mind false positives. We train users that if it is an e-mail newsletter to add it to their black list instead of requesting us to add it to our global black list (one persons spam is not anothers perception of spam). We just received an update that looks at pattern recognition technology, it is really cool. It tightened the screws down with no reported false positives. It just keeps getting better.
Between AV admin, SPAM admin, AdWare/SpyWare/BHO admin it keeps me VERY employeed ;). Yet it keeps getting more and more managable.