We have only seen idle-to-load deltas for both chips IIRC, so you can't really say what the "CPU consumption" was from that.
Of course that we can, and with a very small error margin...
What if Ryzen had high idle power draw because of early/ill-tuned BIOS and motherboard? I don't remember the specifics, but the reported idle power was relatively high, while you would normally expect the idle power of AM4 to be equally or more frugal than FM2+ (There was a discrete GPU, but those shouldn't have dramatic idle consumption today).
Because idle power included the monitors, that s as simple as that, these are full system consumptions wich are measured, because one logically use a PC with a monitor i would think...
If it was a measurement of the load on CPU's 12V rail, it would be different.
The only difference is the PSU losses wich are about 10%, add the VRMs losses, about 10% as well since these are MBs with very good CPU supplies.
Edit : According to Hardware.fr the 6900K plateform use 63W at idle, the CPU idle comsumption is 21W measured at the 12V rail, wich translate by roughly 18W for the CPU, this correlate with Zen wich is said to have in the range of 5W idle power, wich would make for the 13W difference between the two plateforms at idle.
And if my theory is nonsensical, why do you think they disabled turbo, then
Perahps because the final firmware is still not implemented in demo PCs, but for exposing the perf it was better to have a fixed frequency chip, otherwise the turbo would had made it impossible to corner the perf window accurately.