I was surprised that Blogger didn't implement trackbacks. I think to remember to have read somewhere that trackback spam was one of the reasons. And if my experience with News.Profoss is an indication, it might be a valid reason.
Yesterday I had deleted all Trackback spam on News.Profoss, and I was surprised this morning to see, in the admin interface, 12 pages with about 50 trackback spams each. That's 600 spam in one day! On a recent and quite modest website.
I better understand now the decision to not implement Trackbacks. There are spam detection techniques for trackbacks, and I installed it on News.Profoss, but this still takes resources and bandwidth. On a platform hosting thousands of blogs, it makes for a significant resource spilling.
Even some other blogging services like Wordpress implement and propose Trackback spam filtering, I can understand the decision to not propose it due to the spam problem. I'm not even sure I'll leave trackbacks available on News.Profoss. I'm not sure it's worth the pain.