Not the guy you're asking, but thought I'd answer. This may not be referring to true "immunity", but Matt Cutts did say this around the time Panda was first released:

"And we actually came up with a classifier to say, okay, IRS or Wikipedia or New York Times is over on this side, and the low-quality sites are over on this side."

http://www.wired.com/business/2011/03/the-panda-that-hates-f...

So there is something that is specifically recorded for well-known sites that likely prevents them from receiving the same treatment as other, smaller sites. And anyone who works in SEO can tell you that not since Vince has it been just about links.