[Piyush Jain3]

Guys when an update of an app comes why is it not possible to download only the updated part like in android... Why we have to download the whole app again in Windows phone

[ShreyansShah]

i am not sure about android, how it works. but i think, in android also, except a few apps, all the apps have to downloaded completely. i remember updating Candy crush and subway surfers on my wife's S3. had to download full app.
but generally, in all mobile / phone OSs, the apps are in complete bundle formats, not in parts. (i am considering WP, symbian, iOS, WinMobile, etc.)
thus, when u update, u have to do it completely.

[xandros9]

I believe it keeps things simple and more uncomplicated, although delta app updates would be nice.