Requirements for DDR 1600 support is stated, just like you mentioned.
3.Support for DDR3 2200(OC)/1600/1333/1066 MHz memory modules
* To support DDR3 1600 MHz, you must install an Intel® 22nm (Ivy Bridge) CPU that supports DDR3 1600 MHz.
5.Support for Extreme Memory Profile (XMP) memory modules
* To support XMP memory, you must install an Intel® 22nm (Ivy Bridge) CPU that supports DDR3 1600 MHz.
What this is basically saying is the MCH in the CPU and BIOS programming does not support above 1333 reliably.