The whole article is a comprehensive — and thus — saddening look into the future of Twitter clients. What’s odd about the design guidelines is that most are completely arbitrary and seem to have no impact on helping Twitter maintain control of its brand. They just seem to be purposefully annoying. The quoted rule is a perfect example. To Twitter, why does it matter if you only show their username? What possible benefit arises from that?
It’s like a war of attrition: Twitter doesn’t want the bad PR from openly killing third-party clients, so instead they are making developers’ lives harder and harder to make them give up and quit.