What do you do when your company surpasses 100m users and begins cementing its status as one of the internet’s most popular services?

If you’re Twitter, you apparently start adding restrictions to the API that helped you achieve some of your popularity, cutting off functionality offered by other popular services in the process.

On Friday, LinkedIn announced that going forward, its users will no longer be able to display their tweets on LinkedIn:

Consistent with Twitter’s evolving platform efforts, Tweets will no longer be displayed on LinkedIn starting later today. We know many of you value Twitter as an additional way to broadcast professional content beyond your LinkedIn connections. Moving forward, you will still be able to share your updates with your Twitter audience by posting them on LinkedIn.

The “evolving platform efforts” referred to were explained by Twitter’s Michael Sippey, who also published a blog post on Friday explaining:

Back in March of 2011, my colleague Ryan Sarver said that developers should not “build client apps that mimic or reproduce the mainstream Twitter consumer client experience.” That guidance continues to apply as much as ever today. Related to that, we’ve already begun to more thoroughly enforce our Developer Rules of the Road with partners, for example with branding, and in the coming weeks, we will be introducing stricter guidelines around how the Twitter API is used.

Translation: not only is Twitter going to be enforcing the rules it has already created around its API, it is going to be adding new rules that limit what third parties can do with the API. That apparently means companies of all sizes, including LinkedIn, will find themselves without a place in the Twitter ecosystem.

The billion-dollar question: is that a good thing for Twitter?

Dalton Caldwell, the former founder of Imeem and current CEO of App.net, says that Twitter’s strategy is the result of a battle waged within Twitter. He explains:

As I understand, a hugely divisive internal debate occurred among Twitter employees…One camp wanted to build the entire business around their realtime API. In this scenario, Twitter would have turned into something like a realtime cloud API company. The other camp looked at Google’s advertising model for inspiration, and decided that building their own version of AdWords would be the right way to go.

As you likely already know, the advertising group won that battle, and many of the open API people left the company. While I can understand why the latter camp wanted to build an ad-based business, the futurist in me thinks this was a tragic mistake.

Dalton isn’t inspired by Twitter’s ad offerings, and thinks the company could have been so much more. “I believe an API-centric Twitter could have enabled an ecosystem far more powerful than what Facebook is today,” he writes.

It’s clear that we’ll never know if he was right. Twitter’s advertising business is growing by leaps and bounds, even if the efficacy of its ads isn’t yet established.

Arguably, to maximize its ability to deliver those ads requires Twitter to take over more and more of the user experience, leaving third parties using its API out in the cold. But it’s difficult not to believe that the degree to which Twitter is slamming the door in the face of companies like LinkedIn will create significant risks, including the possibility that third party developers will be less likely to work with the company when it asks them to build different kinds of applications, something Twitter’s Sippey hinted at in his blog post.

Yes, Twitter is popular, and has a lot of leverage, but when it comes to how it treats developers, it can learn a lesson from a company that isn’t always on the receiving end of compliments from its developer community, Facebook. That lesson: it pays to have at least a few friends.