Mr. Boutin got snookered by Sergey.
1. The ad server is distinct from the email server, so whatever Sergey Brin says about the ad server does not apply to the email server.
3. Mr. Boutin didn't even mention the fact that Google has no data retention policy for deleted email, or for email on a closed account. How long will these emails be accessible? I don't care if they're on clusters somewhere on some hard disk. What I care about is whether they're accessible by anyone or anything at Google. This a primarily a matter of corporate policy, and only secondarily a technical issue.
Sergey set up a straw man and then Mr. Boutin tried, unsuccessfully, to knock him down.