Google came out with its new comment spam moderation system in December last year. Google+ will immediately identify possible spam and mark it for review. Other viewers won't see the comment; you'll see it grayed out with the option to remove, and the commenter(spammer) won't know the difference. Unless, of course, you decide to remove it. Every time you remove or restore a grayed out comment, it helps train their systems in identifying spam.
The recent changes hide comments marked as spam in a small indicator just beneath the comment count. Check it out:
So, now, the spam comments are hidden to you unless you decide to read them, or mark their appropriateness.