There is some white noise in players H/A spilts. As a whole, players have an OPS about 40 points higher at home. Upton's H/A splits for 2009 & 2010 fall with that norm, Last year he battled a thumb injury all season which could easily explain why we wasn't able to drive the ball (decrease in XBH%,HR% and HR/FB) so you end up with 2011 being the outlier.
Any player moving from a hitters park to pitchers park is cause for concern but I think in Upton's case people are only looking at the surface of what the stats tell us.
I agree to an extent. Certainly most players do have worse stats away from home. We'll see if 2011 was the outlier. I'm not convinced Upton's problems aren't real. If the DBacks do have a long term agreement with Prado, I personally would be much more confident in his long term production than Upton. Obviously, Upton has a high ceiling and could take it to the next level but right now I think Prado is the more consistent player. Simple risk vs. reward IMO.