What I have noticed is that once the official apps/games comes to Windows Phone store many a times the unofficial apps that have a good rating gets removed (Not the case with all apps/games). I think the original creators file copyrights complain to MS. Have a look at some examples below.
Flipkart
Official : Flipkart | Windows Phone Apps+Games Store (India)
Un-Official : Flipkart | Windows Phone Apps+Games Store (India)
Just Dial
Official : Justdial | Windows Phone Apps+Games Store (India)
Un-Official : JustDial | Windows Phone Apps+Games Store (India)
Unroll Me - unblock the slots
Official : Unroll Me - unblock the slots | Windows Phone Apps+Games Store (United States)
Un-Official : Unroll It | Windows Phone Apps+Games Store (United States)
Flipkart
Official : Flipkart | Windows Phone Apps+Games Store (India)
Un-Official : Flipkart | Windows Phone Apps+Games Store (India)
Just Dial
Official : Justdial | Windows Phone Apps+Games Store (India)
Un-Official : JustDial | Windows Phone Apps+Games Store (India)
Unroll Me - unblock the slots
Official : Unroll Me - unblock the slots | Windows Phone Apps+Games Store (United States)
Un-Official : Unroll It | Windows Phone Apps+Games Store (United States)