Apple has increased the over-the-air download limit for the App Store from 20MB, up to 50MB. The reason for this can be The new iPad launch because it includes a high resolution Retina Display which stands for larger app sizes. So from now on you can downlaod larger apps over 3G or 4G networks on all devices.

Developers frequently work hard to keep their apps under the over-the-air download limit, as they believe it reduces the likelihood spontaneous purchases.

Source [macrumors]