I think gaming communities are really making the definition of peer-to-peer murky. Peer-to-peer by definition means there is no central server, and in the case of DRG there is most definitely a central server. The central server just happens to also have a client attached to it. Interestingly, I've never seen Minecraft's open to LAN feature, which functions nearly identically to DRG's setup, referred to as peer-to-peer.
Another interesting aspect is that peer-to-peer also implies that peers are connecting directly to each other. However, I believe  that the connections are technically proxied through Steam's servers, so in fact there are dedicated servers in between "peers", they just aren't doing any of the game processing. This explains why if Steam does any maintenance, you will lose connection to other players in a supposedly peer-to-peer game.
In the end I'm not sure what you'd describe DRG's setup as, I just have to agree it's not simply peer-to-peer as it's always described as.