Nope, not an Apple Dig, this time.
I agree, for Gmail it is opt in, for the those tghat have Gmail.
However, a few people I know do have G Mail accounts and I am prepared to stake a large chunk of my prof' reputation on the following :
Google not only do scan the content of email for 'advertising opportunities' but also scan for the email address of those int he 'to' or 'cc' lists of emails, coming in or out.
Since a collewague fo mine started using a Gmail account, and sending 'stuff'' to my work address, the amount of crud that is hitting my work email has gone up ten fold. To the point where I have set up filteres on my work email to auto bin anything with @hotmail or @gmail.
This is not a 1 April thing either......