People often complain about the unpredictability and capriciousness of Apple's App Store policies yet it's still where developers flock to. Why? Because they make money. Those same policies arguably hurt developers but they definitely help the consumer, which ultimately does help the developer. Tae that as an example of developers not knowing what's good for them.
You see the same thing particularly in tech journalism: people often say the problem with, for example, Windows Phone 7 or WebOS is a lack of developers. No. The problem is a lack of users (and thus money to be made). Developers follow the money.
In the case of Twitter, I think it's downfall is that it is simply a very marginal product and has missed its opportunity to change that. Its usage is a lot lower than the number of accounts suggests [1]. I believe it was envisioned as a way of people sharing status updates in a more public fashion than Facebook. The reality of Twitter (IMHO) is that it's a way of following celebrities.
Twitter clients were doomed before they started, doomed to commoditization then cannibilzation that is. It was naive to go into building on someone else's platform any other way (yet many did seem to believe that Twitter was somehow "different").
I don't believe the existence of these apps is the reason for Twitter's success either. My personal opinion is that people decide to use Twitter and then look for an app to do it. Twitter lives and dies by the success of... Twitter.
[1]: http://www.businessinsider.com/chart-of-the-day-how-many-use...