I'm responding to a two-week old comment here (and made my comment way longer than the single paragraph i Originally intended to post - oops), but Rosberg is much closer to Hamilton than Webber was to Vettel or Barrichello was to Schumacher, in fact he is about as close to Hamilton as Button was (much closer in qualifying, equally as close in races but further off in points).
If Hamilton is one of the Top 3 drivers on the grid then Rosberg is surely in the Top 6, there are probably only 4-5 drivers on the grid better than him (Alonso, Hamilton, Vettel, Ricciardo and perhaps Button), which is in stark contrast to Webber who was never more than a mid-grid driver even at his peak.
If Hamilton was really that much better than Rosberg then we would see it in their relative results and pace, like when Kovalainen only scored half of Hamilton's points.
To put it in numbers as I have a habit of doing, over their 3 years together:
Rosberg has outqualified Hamilton 46% of the time (26-30, as in Rosberg has outqualified Hamilton 26 times out of 56 sessions), finished ahead of him in races when neither suffered a mechanical DNF 41% of the time (18-26) and scored 46% of the team's points (785-911).
I should probably compare this to Hamilton's other team mates for context;
Alonso outqualified Hamilton 47% of the time (8-9), finished ahead of him 59% of the time (10-7) and scored 50% of the team's points (109-109). Under the modern points system Alonso still scores 50% of the team's points when rounded, but actually outscores Hamilton by 1 point (266-265; Raikkonen scored 272 points under the modern system for those curious).
Button outqualified Hamilton 24% of the time (14-44), finished ahead of him 43% of the time (20-27) and scored 51% of the team's points (672-657).
Kovalainen outqualified Hamilton 26% of the time (9-26), finished ahead of him 36% of the time (10-18) and scored 34% of the team's points (75-147). Under the modern points system, Kovalainen scores 35% of the team's points (194-367).
From that we can say Alonso/Hamilton > Button/Rosberg >> Kovalainen. Also of note is that the stats actually support common stereotypes about the drivers' strengths; Button is not a great qualifier, Rosberg and arguably Hamilton are stronger in qualifying than in races, Alonso is phenomenal in races.
For fun, here is how Vettel/Webber stack up:
Webber outqualified Vettel 24% of the time (23-73), beat him 24% of the time in races (20-63) and scored 40% of the team's points (949-1410). Under the modern points system, Webber scored 41% of the team's points points (1046-1514).