It's definitely business - back around the time Gawker got banned from YC for being trashy, there was some amount of opinion that TechCrunch stories should get the boot too - but it was never going to happen because of the exposure TechCrunch gives YC startups.
PG is not going to do anything that increases the quality of news.YC if it in any way could negatively impact YC's bottom line.
So, in some ways, your free speech is moderated by private interests. This is not a critic, just a valid point I think.