reason it looks slightly blurred is because when you move the zoom while taking the picture you are changing the focal length of the lens. The centre of the subject might start out in focus but by the end its not going to be.
If its a true zoom lens (I dont know what lens was used here, but most are at least very close) then changing the zoom doesnt change the focus point.
Some lenses are varifocal rather than zoom, and these change focus as you change the focal length. A lot of supercompact lenses are made this way as its less complex to design. Also some "image quality at any cost" lenses (eg some of the original Vivitar Series 1 lenses, the Pentax FA24-90, some older Zeiss and Leica Vario lenses, some others) are varifocal since the simpler design makes them easier to correct from a designers point of view, sacrificing ease of use at the alter of image quality.
I keep looking at lensbabys and thinking "its so cheap, and it might be a lot of fun, but when would I use it?"
Im bound to end up with one eventually!