Those of us who have spent many years enjoying OS X and using Preview on a daily basis we have seen a child for fourteen years, although we may never have noticed him for more than half a second. Yes, it is the child that appears in the photo of the Preview icon, which leaves us after almost three decades on the screens of our Mac.
Anything else
The elimination of the child in the photo is nothing more than something anecdotal, superficial, a detail. What is really important is the fact that the child disappears, which is none other than the brutal simplicity applied by Jonathan Ive's team to all aspects of Yosemite, leaving aside the elements that simulate reality (also known as skeumorphism) and adopting a much flatter and simpler look, which you can see if you install Yosemite on your Mac as explained by my partner Miguel Ángel.
Throughout OS X Yosemite you can see how Apple has simplified dramatically the operating system, freeing each and every one of its elements from visual load. We can see the windows, the dock, the icons ... absolutely everything has been simplified, taking as an example the excellent redesign of iOS 7 but without reaching the extremes seen in the operating system of the iPhone and iPad.
We cannot forget on the other hand that we are before a Developer Preview at the moment and that Apple usually makes many changes until the final version comes out, so we should not take any information from the visual aspect of Yosemite as final, although it is more than likely if we stick to what is seen in Keynote.