Looking at changes in the initial hand path from the top of the swing. The question is "why"?
2001 (approx): Diagonal
<iframe width="480" height="360" src="http://www.youtube.com/embed/mXWBhaHsAcw" frameborder="0" allowfullscreen></iframe>
2002: Diagonal
<iframe width="480" height="360" src="http://www.youtube.com/embed/sJwPJUnsX8Q" frameborder="0" allowfullscreen></iframe>
2008: Vertical
<iframe width="480" height="360" src="http://www.youtube.com/embed/W8N-N4FEoMY" frameborder="0" allowfullscreen></iframe>
2010: Vertical
<iframe width="480" height="360" src="http://www.youtube.com/embed/1naZag2tDUM" frameborder="0" allowfullscreen></iframe>
2011: Diagonal (but just barely)
<iframe width="480" height="360" src="http://www.youtube.com/embed/wTTKmqmIWVw" frameborder="0" allowfullscreen></iframe>
2013: Diagonal
<iframe width="480" height="360" src="http://www.youtube.com/embed/c24WQ0oKyuE" frameborder="0" allowfullscreen></iframe>
2001 (approx): Diagonal
<iframe width="480" height="360" src="http://www.youtube.com/embed/mXWBhaHsAcw" frameborder="0" allowfullscreen></iframe>
2002: Diagonal
<iframe width="480" height="360" src="http://www.youtube.com/embed/sJwPJUnsX8Q" frameborder="0" allowfullscreen></iframe>
2008: Vertical
<iframe width="480" height="360" src="http://www.youtube.com/embed/W8N-N4FEoMY" frameborder="0" allowfullscreen></iframe>
2010: Vertical
<iframe width="480" height="360" src="http://www.youtube.com/embed/1naZag2tDUM" frameborder="0" allowfullscreen></iframe>
2011: Diagonal (but just barely)
<iframe width="480" height="360" src="http://www.youtube.com/embed/wTTKmqmIWVw" frameborder="0" allowfullscreen></iframe>
2013: Diagonal
<iframe width="480" height="360" src="http://www.youtube.com/embed/c24WQ0oKyuE" frameborder="0" allowfullscreen></iframe>