A referrer spam technicality

This site has been getting a lot of traffic from NewsRiver and StumbleUpon lately, which has created a bit of a quandary. As many of you know, I run ReferrerCop.org, a database of known referrer spammers. For the purposes of ReferrerCop, I've always defined referrer spam as "repeated website requests using a fake referrer URL". Usually, this is done by spammers who want to drive traffic to their sites, but in the case of NewsRiver and StumbleUpon, we have two services sending legitimate traffic, but providing fake referrer URLs.

On the one hand, this behavior is technically against the rules, and part of me wants to classify it as referrer spam. On the other, since the traffic itself is legitimate, webmasters may find it useful to see the referrals in their web statistics, even though the referrer URLs are just generic pages advertising the services. Personally, I find it annoying that these two referrers consistently occupy the top two slots of the referrer listing for wonko.com, yet at the same time I do like knowing that I'm getting a lot of traffic from them.

I'd like to hear what other webmasters have to say about this. Given the circumstances, do you think NewsRiver and StumbleUpon should be excepted from the rule, or should they be considered abusers just like anyone else who sends fake referrer information?