The BIOS downloads often disappear from the OS listing and show under "Others".
Regarding the latest BIOS with the microcode update, I actually don't think that was the "skylake" microcode update. Today I spoke with someone at ASUS that said that microcode update was already in testing and applies to support for some recently released i3 and i5 CPUs. That seems to make sense since the previous BIOS update said "Support 6th Gen Intel® Core™ i3-6098P and i5-6402P processors *Full support of the new CPU requires BIOS version 1402 or later, and VGA driver version 20.19.15.4285 or later". That message was up back in December and the Skylake bug went public Jan 11. Plus MSI and ASRock ran to the media to say their skylake "bug" updates were available.