User blog comment:Silicon Soldier/April Update Has Arrived!/@comment-26625664-20160417160811/@comment-25916964-20160418054858

When compared to the next(current?)-gen consoles, it can be directly attributed to lower resolution textures, and the sort.

When compared to PS3, I can only speculate that it is possibly due to the following...
 * Differences between consoles (PS3 has split RAM where Xbox 360 has unified, software differences)
 * PlayStation exclusive content might not be included in the Xbox 360 game files.
 * Platform specific bug fixes.
 * Different update mechanisms.
 * etc.

Main reason the PS4 and Xbox One updates are so close in size, is that internally the hardware is very similar.