Or they could just be leaving the voltage tuning for the Nano card. From what I recall on the Fury Nano, it didn't seem particularly well binned, just that they put effort into managing the clocks and power which seems software alone can manage the level that the Nano offered. Which would be stupid as it hurts them overall due to how bad Vega looks (although, my guess is they think people don't care that much on desktop performance focused cards). But it gives them an extra thing to tout on that card.
My actual guess, and perhaps this is one of the things that was allegedly causing issues between the CPU and GPU teams at AMD, is that the GPU team sucks at implementing power features in the hardware. They've had stuff that should help with that for a while (and have been adding more and more) but seems like the only things that are actually benefiting power use is the software features (that are just limiting the GPU workload, and letting people tweak power use on their own). If you look at the gains made in the APUs, its clear that the CPU team had better power management (even when they were still pushing voltages and stuff higher than they should be, the APUs still got better in their default states).
My guess is that the voltage issue would be a non-issue if they had the hardware power management features working correctly, but they just have not been. We've seen multiple times now (Vega, Polaris, Fiji, you could argue 290, frankly probably all GCN even although I don't know that AMD was touting efficiency back then) that absolutely the cards are capable of the efficiency AMD states, just that they are not shipping the cards to do that in default state and require you to tune them yourself (and not doing anything to alert reviewers, which is obviously stupid; doubly so since they're leaving performance on the table as well).
