Twitter is nothing if not self-referential. So it should come as no surprise that the microblogging site’s redesign this week got Twitterers talking (2.4 million tweets on the topic to be exact). That’s what it was designed to do — get people talking and eventually, spending more time on the site.

Why? Because the company can use that increased engagement to attract advertisers.

It may be a relatively minor redesign, but more interactive features and multimedia data are all meant to encourage Twitter’s 160 million users to stick around longer on the company’s website.

According to The New York Times:

“[Twitter’s co-founder Evan Williams] has said he was surprised that so many people use the service — 160 million — given how difficult its Web site is to navigate.

That large audience is appealing to advertisers, but the unappealing Web site has not been a welcoming place for them. Twitter, which has raised $160 million in venture capital, has slowly started to run ads called Promoted Tweets that people see when they search the site. Mr. Williams said the new site would improve ads “because there’s going to be more real estate and more engagement.”

Increasing ad dollars are definitely becoming a priority for the once advertising adverse company. As COO Dick Costolo said of the redesign yesterday:

“It’s going to increase the value that people are getting out of Twitter, so in less time you can get more information and value.”

Twitter is working with 16 media content partners — including YouTube, Flickr, Twitpic and Ustream, to encorporate rich media directly into the microblogging experience. As Patricio Robles pointed out earlier today, context is key:

“The new detail pane does more than display multimedia content. Twitter is using it to display related tweets, mini profiles and maps. The pane adds some much-needed context to 140 character tweets.”

Mainly, Twitter wants users to choose the new design of the company’s website over the multitude of third party apps that have been created around the service.

Due to the company’s slow uptake on developing new features, many third party companies have popped up offering extra features to Twitter users. Many users resultantly access Twitter through other sources.

This update is a play to get users coming directly to Twitter.com, and it will help Twitter in the game of catch up its been playing over the past few months. Currently, 78% of Twitter users come directly through Twitter.com. The second most popular avenue is Twitter’s own app (12%), which only launched a few months ago.

If viewers come directly to Twitter, the company can implement all sorts of advertising in and around organic tweets. According to AdAge, Twitter’s COO Dick Costolo plans to start showing the new site to advertisers as soon as possible. As he says:

“The benefit of the new interface is there’s much more opportunity for users to explore. It’s an opportunity for users to engage with the tweet and to see the ways others have engaged with the tweet.”

Users can now see who is retweeting them and track messages more easily. That’s a boon for marketers. As Costolo says:

“We had the ‘Toy Story ‘campaign and back with the old site, they had a link in the tweet that took you to a trailer video for the movie that was on another site. Now, the trailer is right there and so are all the retweets and all the people who have commented on the trailer.”

Part of the reason Twitter has been slow to add new features had to due with its overwhelming growth. Keeping up with user demand has occupied a lot of their time. But for the company to continue to grow, they’ll need to increase user engagement, and that most likely means making  the standalone product better than others that have grown up around it.

That’s the reason that third party developers have a right to be nervous — no matter how many times Twitter claims it isn’t out to destroy them. As Williams tried to do today:

“We made it clear to developers that it’s great for everyone if we make it as good as possible, because that will create more successful Twitter users.”