Exactly, Math Geek nailed it. For instance, let's take a look at the Tomshardware review of the 980 and 970:
As can be seen, that aftermarket 970 hits 177W average while gaming. On the other hand, take a look at the whopping 980 there at 185W for the reference design, and surprisingly coming in lower is the Windforce at 730W. But wait, let's look at the spec page for the GTX 980:
Rated at 165W. So Mousemonkey, AMD is not the only company with underexaggerated power. Nvidia does it, too.