In the early days, the third-party ecosystem was a playground, in which developers could, and did, come up with uses for the service that were never intended or dreamed of by Twitter itself. You like the word ‘tweet’? The bird icon? The character counter? The replies and conversations features? A nice native client on the iPhone? All done first by third-party developer Iconfactory with its Twitterrific app.¹

To me, this is still the very thing that makes Twitter appealing. I’m a happy Twitterrific user, not a happy Twitter user. If third party clients would disappear, it’s very possible that I might stop using Twitter.