It was only today at TechCrunch's Disrupt event that Tweetup (the "AdSense for Twitter") was announced, so Twitter's blog post spelling the end of third party advertising platforms will be very badly-timed news for a lot of developers.
In the verbose post, Twitter's COO Dick Costolo reasoned that because the company wants "long-term health" and "value of the network," they would be updating their terms of services to reflect their changed attitudes towards advertising.
"It is critical that the core experience of real-time introductions and information is protected for the user and with an eye toward long-term success for all advertisers, users and the Twitter ecosystem. For this reason, aside from Promoted Tweets, we will not allow any third party to inject paid tweets into a timeline on any service that leverages the Twitter API."
Twitter launched Promoted Tweets just last month in April, so they obviously have their own fish to fry with advertising on the site. Stopping third party companies—developers who are passionate about the service, and wanting to reap some financial rewards for their work—could spell the end for a lot of apps, widgets, clients and services.
Costolo claimed in his blog post that "third party ad networks are not necessarily looking to preserve the unique user experience Twitter has created. They may optimize for either market share or short-term revenue at the expense of the long-term health of the Twitter platform." [Twitter]