Could turn into another Digg.
You've actually of that opinion about Facebook, but meanwhile, large numbers of people never cease to predict that Facebook will soon control the entire universe. So, opinions vary.
However, twitter gave away control to 3rd party clients. Only a tiny number of twitter action comes from twitter.com.
When most of your userbase uses 3rd party clients, you have very few monetization options.
Reference: http://blog.twitter.com/2010/09/evolving-ecosystem.html
Twitter could always restrict their API, too, to discourage or make some third party tools obsolete. This would only be accepted if they made their own available with applications similar features and quality.
Twitter is actually doing a great job of blocking spam - I used to get a few spam followers a week, now it's rare.
I follow a lot of programmers and project leaders on Twitter and your analysis, as well as the one above, are dead wrong. I constantly hear about news and see good links on twitter hours or days before they show up on places like HN or Reddit.
