You also have to consider that this is just from one season. In 2011 Fielder had the biggest difference in home and away splits, so if he continues the trend he started last year, then yes it looks like Comerica Park will drain some of his power. However, if you look at the other 5 full seasons he played with Milwuakee, you'll notice that his home/away splits arent nearly as dramatic as last season would indicate. I'm gonna give Prince the benefit of the doubt on this one, and I'm expecting well over 30, if not 40 home runs.
And as mentioned earlier in this post, Fielder IS a legit .290 hitter, and he gets his share of walks. So even if the home run total DOES drop off a bit, he will still produce in the other categories.
You still have to remember that Prince does Have a career .279/.381/.515 avg/obp/slg outside of Miller Park, so I think he's pretty safe.