the cover doesn't matter at all.
that's just the artwork a retailer chooses to display the game.
there are 2 editions available:
the standard edition is the base game.
the Special Edition is slightly more expensive and comes with additional content, particularly for multiplayer.
there have also been 3 patches released so far, fixing bugs and even adding an editor. the latest is v1.03. but that shouldn't concern you as you can download the patches for every edition of the game. if you choose to go with Steam, it'll be updated automatically.
BTW: digital retailer
http://www.getgamesgo.com/ is currently running a promotion on the entire franchise. both editions of MoW: Vietnam are currently 25% off.