iOS Developer Library (Technical Q&A QA1779):

Starting with iOS 6, the app store will automatically produce an update package for all new versions of apps submitted to the store. This package is optimized for updating an app from one version to another, and contains files that have changed between the prior version of an app and the new version of the app, excluding files that have not changed.

When used optimally, an update package is significantly smaller to download than the full package of the app and the update will install more quickly. Also, in many cases, this mechanism allows updates to large apps to be downloadable over cellular networks where app downloads are subject to a size limit.

Rupanya Apple sudah secara “resmi” menerapkan sistem delta update untuk aplikasi pihak ketiga pada App Store.

Yang saya tahu sebelumnya, Apple memang sudah menerapkan sistem delta update ini sejak iOS 5, tetapi khusus untuk OS saja bukan aplikasi.

Seandainya APT sudah mendukung delta update, mungkin @saurik akan menambahkan dukungan delta update untuk Cydia. Tapi sayangya belum.