Open Radar

 
Downloading an app for the first time requires you to download the entire binary file. This makes sense. Downloading apps over wifi restricts downloads to apps less than or equal to 20 MB.

Updating an app requires the entire app binary to be re-downloaded. This should only download what has changed, just as iOS & Mac OS updates download only what has changed.

For example: I'm downloading an update to Weather HD again and it takes 284 MB which is right around a quarter of a gigabyte. If vimov llc who makes Weather HD changed 1% of the app by contribution to file size (perhaps by implementing Twitter.framework support and fixing bugs) then I have to re-download 281.16 MB.

But if iOS and iTunes can only download the bits that have changed, then updates can save huge amounts of summed bandwidth. This is an extreme example, but if only 1% did change I would download only 2.84 MB compared to a gargantuan quarter of a gigabyte. 

Reducing the download size by implementing delta updates will result in better battery life on devices (network use vs. combining delta parts of an app file), faster download speeds, user ease of use, saving of bandwidth for Apple iTunes servers and user devices and more app updates. Additionally users would be able to update more apps over cellular connections and may be more inclined to frequently update. Users solely dependent on cellular connections would be able to update their apps more frequently also.

Similarly to the way that delta OS updates are better for iOS users, delta app updates are would be great. All of these benefits will also apply to Mac OS users updating apps through the Mac App Store. Delta app updates would be an excellent performance enhancement as they reduce network use.