I wonder about the legal aspect of this, since Diplomacy is a fairly modern game. Do they have permission from the creator of Diplomacy? Or is it fully legal to take a board game and make a web version of it?
In our case, we really do encourage people to go buy a copy of the board game, preferably from your local nerd shop. There's a lot to recommend playing Diplomacy online (I believe it was the second game playable by mail published after chess), but there is something special about playing in person and having all the physical materials.
I made a website for a fork of UNO years ago called "Hot Death UNO" and was sent a cease and desist from Mattel for it. I changed the name and the look of the cards and poof, no more problem.