Regarding the two flower pictures, they look virtually identical to me. It is possible the camera is too close for the autofocus to actually focus, in which case it will always take a slightly blurry picture. It's also possible that your particular lens is simply soft at that zoom, or that the you didn't hold it steady enough.
With shots like these, only a very small portion of the picture is ever going to be in focus. The automatic setting on the camera will select a very shallow depth of field (probably, mine would) and you probably have it zoomed fairly far in, so only whatever the focus is actually on will be really sharp. In this case, I assume the focus was on one of the front two petals.