Fooling with Focus

I thought Kim's shots with the macro lens and its very specific point of focus were interesting http://picsbykim.blogspot.com/2010/04/macro-fun.html. Thought I'd try a slightly different experiment of my own:

Focusing on the center of the lower tulip...
Focusing on the center of the upper tulip...
Still never got the whole center of either one in full focus. What's that about???? (Most likely the inexperience of the person behind the lens)...