To follow up my last post with a much less philosophical one, I also understand Twitter's reasoning for their new API rules. Even some of the controversial ones, like the Display Guidelines.
It makes nothing but branding sense for Tweets look consistent regardless of what environment or scenario you encounter them.
Tweets are the Twitter service's product. They're what users make and produce and share and interact with, and they're what the vast majority of Twitter's users would identify as synonymous with the service.
It makes as much branding sense for Twitter to establish global visual consistency with their product as it does for other companies, like Coke, or Apple.