I don't get this:
The article on sensor sizes seems contradicts the articles on depth of field and focal length.
The sensor article says that since larger sensors require you to move closer to the subject or use a longer focal length for the subject to fill the same portion of the frame, a smaller aperture would be needed: Larger sensors have shallow depth of field.
However the articles on DOF and focal length say that focal length does not change depth of field significantly if the subject occupies the same amount of frame: large and small sensors would have the same DOF if the subject occupies the same amount of frame.
Also, you could argue that a cropped sensor is just that: a cropped version of the image that would have been taken by a full frame sensor. Since cropping a picture does not change depth of field, why would the use of a smaller sensor?