Dealing with human players can be frustrating when you keep losing over and over. Giving an NPC now and then gives a human player who has lesser cards then people of similar rank a fighting chance after several defeats.
While I personally prefer to play against NPCs (I'm not the competitive type, and mostly play campaign), I think there should be some changes to NPCs in MP: They should give less ranking points (or even none at all) than beating another player. The ranking system should, once there are enough players, make sure that you play against other players of your level of skill and gear. By winning against an NPC, you'll get paired against a stronger human player in the next game, which probably isn't what Ultreos is asking for.