In a different age (no KERS and DRS) Rosberg would have already won the WDC on account of having less DNFs.
You need to remember that under the old points scoring system (90s and earlier) a driver can drop a result or two from each half of the season depending on the number of races. This instantly widens the gap between Hamilton and Rosberg.
However, we're where we are and I don't believe for a second that Hamilton has dominated Rosberg, but I think he's shown that he has much better race craft than Rosberg, and that if the Mercedes wasn't so dominant (IE a guaranteed 1-2 in the absence of mechanical issues) then it's also likely the points gap would be wider. Although in all likelihood would Hamilton have come through the pack as strongly as he did? Doubtful.