I don't know.  For any number of reasons.  Maybe it's got better balanced gameplay.   Maybe it's got a better score.  Maybe it's better when played on a big screen.  Or maybe the Wii version is no better than the PC version.  I never said it was, after all.  My exact words, in fact, were, "I've only played it on the Wii and it's fine.  It's a lovely game."  I have no idea whether the Wii version is better than the PC version.  But I do know that the Wii version plays very well, which is why I love it, and why everybody else who has played it loves it and why IGN picked it as the Wii Game of the Year.