Earlier quoted context omitted.
Could Matt do that - sure. Would he do that straight away, faster than the results can be captured, or does he have constant monitoring of his page - I doubt it. Still - nobody even tried as far as I can tell.
I don't know. I'm sure tons of spammers already target Matt's site (they all hate him). Google probably already has some kind of special exception for him.
The more negative SEO that happens, the more data that gives Google. Overtime, the negative SEO sources will be over-saturated, offering no benefit for either positive or negative SEO.
Driving down the positive and negative value of links makes all SEO link building efforts consequently worthless. Which in turns increases the importance of other ranking factors.
This is a natural evolution, in tiny tiny steps Google is nudging people into playing it's game - producing websites that have content. SEOers are slowly falling into line building private link networks, paying people to write content, afraid to spin/rehash existing content because it might leave a fingerprint Google can detect.
It's fascinating watching.