Vertical buttons make more sense than horizontal buttons. See (common) traffic lights:
<http://www.google.com/images?um=1&hl=en&safe=off&biw=1440&bih=723&tbs=isch%3A1&sa=1&q=traffic+lights&aq=f&aqi=&aql=&oq=&gs_rfai=>

They removed the 'iTunes' app name from the navbar (meaning the buttons had to go somewhere else) AND in moving them shaved something like 20 pixels off the height of the navbar. Apple makes these refinements all the time.