That's what I thought would be the case before I cracked into some numbers. You can look at the data for 2010-2012 players here (min 1000 Innings):
https://docs.google.com/file/d/0B5pI...it?usp=sharing
Although SS will have more balls hit to him, there is just as much variation from the mean in terms of balls fielded, as with LF. This is the case whether or not you include out of zone balls in your totals. (Previously I just looked at in-zone opps and plays made).
For LFers:
For SSs:
When you think about it, its not surprising. IN today's game, Brett Gardner, Ben Revere and Juan Pierre are playing in the corners. Meanwhile Derek Jeter, Ricky Weeks, and Dan Uggla have MI jobs. Things have leveled out.