Because Google is well known for deleting data rather than storing and mining it?

Not sure how that's relevant to "Once your emails get into google servers, the NSA has made a copy of them. NSA copies your emails before you even read them"?

Also, please explain how you would implement a webmail service without storing emails.

It's relevant to the idea that if an email enters Google, it's probably accessable to the NSA, even if you delete it. I was directly responding to:

"is it indisputable fact that the NSA has all your email, or, is it more like, we can't be sure what they do and don't have access to"

They don't need to have second hand copies of the mail when they can just tell Google to give them access.

"implement a webmail service without storing emails." is not relevant to anything I said.