Yes, an information for site owners why they are blocked would be great. But I don't know how we could implement this in a good way. If someone has Ideas in this direction I would love to hear them!
If the stats are shown historically, a site owner could see that after a redesign or some changes on their site, or maybe after signing up with a new ad vendor, that there was a spike in their ad blocks and rethink their design or deal with said vendor.
I don't know if any of this would play out as I'm visualizing it, but I do feel opening up the conversation between site-owner and visitor to figure out what can be considered useful advertising is good for everyone.
[0] http://adblockplus.org/blog/an-approach-to-fair-ad-blocking