You have to assume Joe Posnanski is making a ton of money.

Why else would he have left Sports Illustrated, where he was arguably the magazine’s highest profile writer, for the new Sports on Earth, where he was that site’s highest profile writer, only to depart a few months later for NBCSports.com, where he will be that site’s highest profile writer?

Follow the money, right?

NBC made it official today, announcing that Posnanski will be its national columnist for NBCSports.com. In addition, he will also contribute to GolfChannel.com, NBCOlympics.com, NBCSports.com’s SportTalk blogs, including HardballTalk, as well as to the websites of the NBC Sports Regional Networks.

NBC has branded his weekly Friday column as “The Big Read.” His debut entry is on Alex Rodriguez.

Clearly, NBC hopes Posnanski’s name recognition, not to mention talent, will helps its site gain more of a foothold in the crowded digital sports arena. I’ve heard some people complain that his luster has been diminished by the backlash from his book, Paterno, which met with some harsh reviews, including one from this corner. There might be some truth to that, but I think time has a way of smoothing over the edges.

If you’re Posnanski, the bigger question is: Will people still read my stuff? He had a huge platform at Sports Illustrated. Not so much at Sports on Earth, and NBCSports.com faces stiff competition from the other network entries from ESPN, CBS, and Fox, not to mention Yahoo! Sports and The Sporting News. People have to find him first before they can read him. It will be incumbent for NBC to pump up the volume for its newest addition.

All writers have an ego. Posnanski didn’t do a piece on Rodriguez, which meanders over three Internet pages, just to have it drift in cyberspace. He wants readers to consume that story.

Financially, I’m sure Posnanski has done very well for himself. As for whether his voice will remain as powerful at NBCSports.com, well, that remains to be seen.