I have a DZ68BC. This board has also a 'fast boot' option with 3 sub options. One of these suboptions is to perform no USB initialization. When I disable this option I get the same behaviour: USB keyboard doesn't work until the OS takes over.
The help text describes that this is the case and also that this option is disabled when a boot password is active, would be difficult to enter a password without a keyboard :-) The help text in the DZ68BC bios does state that the only way to get back into the bios is to power off and the hold the power button until the beep (which works).
Displaying not the 'press F2' on the boot screen would indeed be an improvement (but there is also a separate setting for that).
As entering the bios is not a daily activity, this feature has some benefits.
That's one way of looking at it, but I'd rather have the option to hit F2 without going through the power-off dance, even if the BIOS splash screen isn't shown at all with certain optimizations enabled. So I haven't enabled any of the three optimizations, but I did find one that slashes the amount of time spent on the BIOS splash screen, and that's good enough for me: disable the Marvel SATA controller. You're probably not using it anyway. If you are using it, you probably shouldn't be.