The bump in over-the-air downloads comes on the same day that Apple released iOS 7, and two days prior to the iPhone 5s and 5c public launch. The new iPhone 5s in particular will likely spur development of advanced apps looking to take advantage of the handset's buffed specs.
With the new cap, Apple is likely preparing for a new breed of app expected to address the iPhone 5s' raw processing horsepower generated by a powerful 64-bit A7 SoC. Developers are already testing boundaries with titles like Infinity Blade III, which uses a refreshed graphics engine to create extremely detailed 3D environments and smooth gameplay.
As apps become more capable, their size usually increases with data for rich environments, powerful features and slick user interface tweaks.
The change is seamless and will only be noticed when attempting to download a 100MB+ app over a cellular network. As always, no cap is applied when purchasing over Wi-Fi. The App Store OTA limit was last raised in March 2012 in preparation of apps built for the third-generation iPad's Retina display.