[pmelendez]

taude already explained it but I will add my two cents. With widgets the look depends on the developer, which I found annoying when I had an android since I had to go through several screens just because some widgets where really big.

Live tiles are "free", they are the same icon that you would use to start the app and the look and feel is more uniform and rearrange between them in a more convenient way.

Also you can pin a lot of app specific items. For instance, from the people hub I can pin a tile of the whole app and/or pin specific people, and when you do that the tile itself seems like a different app. In my wife's tile I can see whatever she posted on Facebook or twitter, and also it serves as a shortcut to publish something on the wall, or to call or text her, it's just very convenient!