I think specifically it must run through Android's own storage access system: http://android.stackexchange.com/questi ... rd-content
Expecting users to root and modify that system file looks like it will no longer solve the problem (if anything requiring root and modifying system files can really be considered a solution in the first place.)Since 4.4 the "WRITE_EXTERNAL_STORAGE" permission no longer grants WRITE access to the secondary(external) sdcard. (This is a simplified explanation, 4.4 did not force this change.)
The necessary permission to do so ("WRITE_MEDIA_STORAGE") is only avialable to system apps.
Since 5.0 it is possible to gain write access through Androids storage provider system, this must be implemented by the developer though.