Easy there tiger.
In 2007, Hamilton finished on identical points to Alonso (who is widely regarded as the best driver in F1.
In 2009, he finished ahead of his team mate.
In 2010, he finished ahead of his World Champion team-mate. Only Alonso and the ridiculously fast RBR cars could beat him.
As shown last year, by finishing in the top 4, Hamilton showed that he could only be beaten by the RBR cars and Alonso. Nobody else could beat him over the course of a full season.
I assure you, this is the same Hamilton we are seeing in 2011. Right now, he is suffering from bad luck and a dip in form. No driver can maintain top form for the whole season. As the season progresses, I expect to see both Alonso and Hamilton move up the WDC table.
At present, I would only rate Alonso ahead of Hamilton and I think Vettel and Hamilton are about the same (Vettel has really raised his game this year).
As long as Hamilton drives as he did in 2007, 2008, 2009 and 2010, he will confirm his position as one of the best drivers in F1.
And with regards to why Button would move to Ferrari...because its Ferrari and also the big salary.
As Button's retirement looms, he will look to finish his career on a high salary (this applies to most sports people).