Apparently, they had to reign in the fire thing a bit for gameplay reasons because in an early build, a playtester started a fire, ran to another part of the map, came back an hour later and found out that the fire had spread so far it had killed the final boss of the game. So apparently, it's not a gimmick. The weather system is apparently pretty neat too. It's interesting how though Far Cry 2 is still very much a technological showcase like the original, the new developers are focusing on different applications of that technology rather than 'omg these textures'.