Spammers Giving Up? Google Thinks So

According to Google spam is flat for the first time in years. While this Wired article suggests this may not be the case, it did get me thinking about how Gmail's spam filter manages to work so well. A bit of Googling uncovered this video featuring Brad Taylor, Google's spam czar. Anyway, as I expected, every time you hit the "Report Spam" button in Gmail it sends the message to some central database which then ensures that message is marked as spam for others. That got me thinking, if Microsoft (with Hotmail), Yahoo! and Google (with Gmail) all got together and created a giant spam database couldn't they basically knock out spam completely? Why, other than the competitive advantage a company's spam technology offers them, wouldn't they do that for the good of humanity?