of course nadal still did more in a half season he played but he already won the award a gazillion times plus he missed half of the year.
so I think it's OK to vote for ferrer just for the change and to reward his hard work. really amazing how he could improve in his late 20s despite having a classic "young players game" (most grinders flame out in their mid 20s like hewitt, courier, wilander and many others).
despite having limited weapons he worked on his weaknesses (takes the ball much earlier now and has a better albeit not spectacular serve) and still keep his strengths.