I'll let Google explain the exact same product decision for their social network Orkut in 2009:

"Mass exportation of email is not standard on most social networks — when a user friends someone they don’t then expect that person to be easily able to send that contact information to a third party along with hundreds of other addresses with just one click. In order to protect user privacy, we now exclude email addresses from the CSV export file."

http://techcrunch.com/2009/10/26/orkut-slows-hemorraging-to-...

They're right. Programmatic export of friends' email addresses is too ripe for abuse in the world we live in.

I just hope that Google+ keeps the "Google Takeout" feature and doesn't close up. "Openness" was Google's selling point for Android when it first came out, and yes, it's still "open", but nothing like what it once was. This just seems like a deja vu waiting to happen.