I think it would be loss of authenticity, and I am sure Apple can afford to pay more than could pay himself at Anandtech. At the very least, he no longer has to worry that his paycheck might ever bounce. The concept of "selling out" has always been a murky and subjective one, and it usually has as much to do with the values of the observer as the actions of the subject. But in a case where someone had been arguably on the side of the consumer for many years and presumably turning down lucrative offers in order to tell the unbiased truth, and then suddenly accepts one of those offers, well, it looks sort of like selling out.
Now, I'd be a hypocrite if I tried to make that case myself, because I stopped reading Anandtech a couple years ago, and I couldn't with a straight face demand that Anand care more about it than I do. I stopped largely because the news got dull and repetitive once 1) Intel decisively won the CPU war, and 2) the GPU market became a permanent stalemate between AMD and nVidia (plus a little bit of Intel). If Anand basically retired because there was no longer an interesting story to tell, well, I can relate to that.
Loss of objectivity, maybe - I mean, I don't think we'll see him publicly praising Samsung smartphones any longer! But authenticity? You think he's going to be doing things he doesn't care about or believe in at Apple?
I think you may not be familiar with how "sellout" is commonly used. It's commonly said, e.g., of musicians when they make a popular song, for violating their assumed allegiance to being "true" to something other than career. It's more about an abstract idea of what someone or something "stood for" than about the actual person, and it takes place in the minds of observers more than anything.
I don't think what he does in his work for Apple has anything to do with it. If he tried to go back to the Anandtech style of journalism, I think he would lack credibility now that he has accepted a job at Apple.
Now, I'd be a hypocrite if I tried to make that case myself, because I stopped reading Anandtech a couple years ago, and I couldn't with a straight face demand that Anand care more about it than I do. I stopped largely because the news got dull and repetitive once 1) Intel decisively won the CPU war, and 2) the GPU market became a permanent stalemate between AMD and nVidia (plus a little bit of Intel). If Anand basically retired because there was no longer an interesting story to tell, well, I can relate to that.