Thanks to iFixit, we now know that the Sony PlayStation 4 features a secondary ARM based processor and a 2 Gb RAM chip alongside it. Note the 'b' being lower case, meaning the RAM chip's capacity is really just 256 MB (DDR3 SD RAM type, as per the teardown report). Remember when 256 MB RAM was all a CPU or GPU had in a console? (Hint: the PS3).
While the ARM chip has many tasks, mainly background tasks which are carried on even while the main APU is powering a game or even an app. Word is that H.264 compression is carried out using the secondary processor (for the 15 minute video loop). ArsTechnica discovered that the main APU is utilized when you're downloading a large file, which causes the PS4 to consume as much as 70W of power during the task. Perhaps the ARM chip is already too overloaded with many other things to be buggered with the task of downloading. However, if Sony were to have taken the other road, we could have seen figures close to 20W (or even lower) while a download was in progress.