In Dhoni’s case, the ball dropped just in front of his gloves, there is a 50-50 chance that he wouldn’t know if he has caught it cleanly or not. So, let us give the benefit of doubt to MS and I apologise to all the viewers for the inclusion of this clip. Overall, you cannot question Dhoni’s sportsmanship because he is the type of batsman who walks when he edges the ball to the keeper.
But as for all the other cases, they were all deliberate actions in which the fielder was totally aware of the situation including the Campbell incident.
Source : Official Cricket