Update 2011-02-23: ÜberTwitter is now ÜberSocial, and is up again: UberSocial, formerly UberTwitter, and Twidroyd now back online
Twitter has been docile for a long time regarding branding and competitive issues, which has left the field open for establishing an ecosystem around it with a lot of complementing services with Twitter-like names and revenue streams of their own. There are complementing services that make much more money than Twitter, e.g. multimedia tweet providers, ad providers, analysis providers etc, while Twitter hardly makes any money at all.
It seems Twitter’s patience is over.
When these things happen it tends to be for financial reasons, and in this case it’s easy to guess it’s about protecting upcoming revenue from ads.
we ask applications that work with Twitter to abide by a simple set of rules that we believe are in the interests of our users
API Terms of Service – dev.twitter.com
Twitter Help Center – Guidelines for Use of the Twitter Trademark
Display Guidelines – dev.twitter.com
Twitter has to realize that the value of Twitter is to a large extent due to the ecosystem around Twitter, created by other companies than Twitter. Twitter itself is very easily copied, except for the amount of users of course, and many users don’t even realize Twitter just provides distribution of 140 character long text messages and a third-party API, and really nothing else.