Posterous has announced it’s shutting down its platform April 30th, as it’s Founder and CEO Sachin Agarwal said that they’re focusing their efforts 100 percent on Twitter. That’s a massive mistake – not focusing on Twitter, but that they have to give up 4 million content producers in the process.

In fact, the more I think about it, the madder I get – not for me, as I’m not a Posterous user, but for the fact that it is a slap in the face of good Internet business logic to just toss out content like that.

Let’s forget for a moment that one should never count on just a single social media platform to use for blogging or other types of content, and for this reason presented front and center: if the platform closes, you have to start all over again. Let’s look away from that for a moment.

Let’s look to the fact that every Posterous blog posts presented a chance to be melded into the Twitter plaform, and in such a way that a Tweet could readily open up to a Poterous page and in tern that page could be integrated with a Twitter photo, if the content developer needed to do that.

And then the Posterous blog platform could be the ad-serving base for a new, expanded Twitter system.

All that opportunity’s missed now, and it’s not even clear the Posterous and Twitter people were ever working toward that. Moreover, it’s not even obvious that Twitter was working in the direction I’ve described – it should be.

Consider this March 12th 2012 Twitter Blog post:

Today we are welcoming a very talented group from Posterous to Twitter. This team has built an innovative product that makes sharing across the web and mobile devices simple—a goal we share. Posterous engineers, product managers and others will join our teams working on several key initiatives that will make Twitter even better…Posterous Spaces will remain up and running without disruption. We’ll give users ample notice if we make any changes to the service. For users who would like to back up their content or move to another service, we’ll share clear instructions for doing so in the coming weeks.

Twitter has zero intentions of hanging on to Posterous, and they made that clear last year.

The current Twitter design is monetarily not efficient, and watching Twitter engineers try to pry revenue out of the current design is an eye-watering experience. Posterous offered the content and platform that pointed a direction to a more perfectly multi-media future for Twitter, where it became possible to build a giant network around both Posterous and Twitter users, and then allow for the melding of tweets, blogs, photos, and video.

That chance is gone.

I hold that Twitter is vulnerable to attack by a new competitor that is designed in the way I point to. One who’s design leads to better monetization and that has a plan for the rapid acquisition of users. Twitter had better hurry up and get on the task of making its next phase, before it’s too late.

Indeed, if the Posterous issue is any indication, it may be.