Twitter's transition from hyped start-up to profitable mainstay is causing angst for its third-party developers, which have built a thriving ecosystem of URL-shorteners, iPhone apps and other services around the popular microblogging platform.

Venture capitalist and  Twitter board member Fred Wilson issued the first salvo when he urged developers to stop "filling holes" and start creating "entirely new things." His post was interpreted as a message that the microblogging service may put third-party services out of business by building similar services internally.

Then Twitter bought Atebits, the maker of the popular Mac and iPhone Twitter application Tweetie, which it will now make available for free.

The moves created some drama among some developers ahead of Chirp, Twitter's first official developer conference which will be held this week, but the change was "entirely predictable," writes angel investor and tech-blogger Chris Dixon:

The real problem is that somehow Twitter had convinced the world they were going to "let a thousand flowers bloom" - as if they were a non-profit out to save the world, or that they would invent some fantastic new business model that didn't encroach on third-party developers. This week Twitter finally started acting like what it is: a well-financed company run by smart capitalists.

The shift in Twitter's growth is good for developers, argued Marshall Kirkpatrick of ReadWriteWeb:

Tonight's news demonstrates again that independent developers can code their way into cash, equity and a job at one of the hottest startups on the web. That bodes well for those of us who love to use the software built by all of them, too.

The Atebits acquisition could lead to Twitter screwing up a fine app, Daring Fireball's John Gruber warned. And, he said, "there's going to be some heavy drinking tonight" by the developers who built also-ran iPhone Twitter apps.

The severity of their hangover will determine the next chapter for Twitter.