I don't expect multiplayer to be downgraded in other games, but it certainly is in this one (which makes this port inferior in terms of gameplay).
Multiplayer is the main fun part of Most Wanted because singleplayer in this game consists of mostly uninspired and boring repetition: There's pretty much no variation in race types, there are the same five events for every car in the game.
Multiplayer, on the other hand, has plenty of interesting and creative challenges that provide a stark contrast to the monotony that is singleplayer. These challenges are also much more fun with more players being involved as they aren't all races (which also profit from more players, especially team races).
And, yes, the PS3 and 360 versions are downgraded in terms of player count compared to the PC version: It's a much more lively game with 12 active racers in a session. But the Wii U version is going down to pretty paltry numbers.