There have been some articles in the Japanese press misinterpreting this announcement and generalizing it as some sort of ban on advertising by Twitter. There have been some allegations that this new policy change would cause problems with the Twitter related activities that Digital Garage engages in.
As the Terms of Service and the announcement say clearly, Twitter continues to encourage advertising around Twitter and is encouraging innovation. The key is that the advertising should not confuse or add friction to the experience of the user.
All of the current advertising that Twitter Japan/Digital Garage engage in is consistent with the guidelines presented in the announcement by Twitter. Digital Garage works closely with Twitter in developing innovative and new ideas for helping companies communicate with their fans without hurting the user experience.
Digital Garage has a very close and broad operating level relationship with the US Twitter team and Biz Stone recently joined the advisory board of Digital Garage to help Digital Garage continue to innovate with Twitter and in social media in general.
Japan has been a very interesting testing ground for new services and ideas around Twitter and advertising and this current announcement by Twitter reinforces Twitter's (and Digital Garage's) commitment to focusing on user value and is primarily intended to try to prevent product degradation by advertisers and service providers who fail to have this focus.
Disclaimer: I haven't spoken to Twitter management about this blog post and this is my interpretation based on reading the releases and talking to the team in Japan. I'll be speaking to them soon to update this post if they have anything to add, but I wanted to get this out there to correct some of the crazy assumptions in the main stream media in Japan.