CNN says maybe.
In my somewhat-informed opinion I think that Ari left because he found himself too far inside the Plame story to credibly answer questions. The ‘ongoing investigation’ excuse did not exist yet so if someone came up with a real zinger or a juicy scoop Ari would have had a hard time dodging effectively. He was there, he was a player and he never knew whether the questioner had some killer follow-up in store that would belie whatever dodge he might think up. Did something similar happen with Scott McClellan? Who knows. The scandals have grown so thick you wonder whether they can keep up.
For me the emblematic story of McClellan’s tenure was his gleeful stonewalling of the Plame story on the basis of prejudging an ongoing investigation. It frustrated the White House correspondents by basically shutting them out of the story and leaving meaningful developments to freelance muckrakers like Murray Waas (on whom they took revenge by ignoring his scoops), but at least it has a sort of internal logic. It did, anyway, until the president openly prejudged an ongoing case to help a political ally. You could say the same thing about any post in the administration at this point, but trust and credibility have eroded so badly for McClellan that it would probably be best to give someone else a fresh start at the job.
Speculate about whether CNN has it right, theorize about why Mac got the boot and share your favorite Scotty stories in the comments.