Risk. Politics. Life.

What I like about Diplomatic Risk as opposed to regular Risk is that, like in real life, it is NOT everyone's goal to dominate the entire world and destroy everyone else. Instead, each group has their own specific goal, that may or may not involve war, and may or may not come into conflict with certain other groups' goals. It is far more realistic that way - and makes alliances more possible and more trustworthy than in normal Risk. Every group has their own goals, and working toward those goals is working toward their own self-interest. Self-interest does not necessarily mean conquering a lot of territory.
The game is much more fast-paced than in real life, obviously. Alliances are not so quickly made and broken, war not usually so suddenly declared, and it's highly unlikely that a plague would not be able to be contained to one continent (unless of course, the plague is actually zombies like we've been saying all along). The secret powers that each group has is also kind of unrealistic. Those powers get really extreme, and unlike in real life, there's no chance of them failing. Also, another large difference between the game and real life, is that the groups that were formed had no previous loyalty to their group or color. That probably made it easier to cross nationalistic boundaries and form alliances.
I don't know how much communication is an issue in real life, but I've definitely observed communications failures between the diplomats and heads of state - whether it's the diplomats not carefully studying the board before making decisions, or the heads of state deciding to do something other than what the group agreed on. I'm guessing that there's more accountability in real life, and there is also more time to formulate and clarify any plans.