The difficulty here is that what we have isn't an official statement from Google, but something that was said by Matt Cutts in answer to a question, recorded, and subsequently published.
I haven't seen any clarifications from him appear anywhere since, and naturally there is going to be all kinds of speculation as to what will actually happen.
Interestingly, although as you say Google has covered the keyword stuffing issue, he made reference to it in his answer, saying (with reference to those that abuse SEO) "like too many keywords on a page".
Also of course he made reference to "or exchange way too many links" but I thought that was meant to have covered already as well. So I don't see this statement as a policy change but rather as an enforcement of those guidelines which already exist, with perhaps some tightening of them as well. Google has advised against "excessive" link exchanges for a long time but the fact is that there are still very many sites who are doing well and have dozens of link pages containing hundreds of links to anyone who will exchange with them.
Likewise in another thread I gave an example of keyword stuffing on my own site (which I have now addressed
) which until now had not been penalized but perhaps could be with this coming update.
To me this is rather like when the police clamp down on a particular crime in an area. The law against it and the penalties are already in place, but it has grown to the extent where they feel the need to devote extra resources to combat it.