I'm not a big fan of the term "friends with benefits" either. I prefer "intimate friends" more. To me the term has become too derogatory and indicates that there are no benefits to anything else but sex in these particular friendships. Like its not a benefit to have a friend you like to play tennis with or something. The term makes it sound like they are just a benefit if you want to have sex with them.
I tend to think that poly people are more likely to have sex with friends or at least be okay with it though. So why hide it or not say anything. Really, if everyone is consenting then it shouldn't be a big deal I don't think.
I think there is little difference from FWB/intimate friends to poly relationships other than level of commitment really. Bottom line is you can call your relationships whatever you want as long as you are both understanding where each other comes from. Here's to friends *clink.