Sport is sport...you don't rise to the top in any sport unless you have a lot of talent
and you take maximum advantage of it, and it is hard to stay at the very top year-after-year-after-year-after-year. Seemingly-steady progression is therefore the exception, not the rule...much more common is for people to have more "checkered" careers, with flashes of brilliance interspersed with periods of lesser performance due to, e.g., injury, changes in motivation or goals, etc.
Case-in-point: many here want to point the finger at Wiggins for doping because of improvements in his performance
relative to others, e.g., Tony Martin. Yet, Martin himself doesn't seem to consider his 2012 season as a valid benchmark that would allow such conclusions to be drawn:
http://velonews.competitor.com/2013/02/news/martin-poised-to-rule-the-clock-in-2013_274593
So where is the evidence that Wiggins markedly improved his power last year? The answer is, there doesn't seem to be any...his self-reported powers are consistent with his historical data, he didn't go up any climbs especially fast, and the fact that he was now able to beat others he hadn't before (e.g., Martin) could simply be due to the fact that they went backward.