This is what it says on the page:
Positional eligibility is based on 2010 statistics. For hitters, a player must have played 20 games at a position to be eligible there in 2011. For pitchers, starting pitcher eligibility is achieved by having made at least five starts in 2010 and relief pitcher eligibility by having made at least 8 relief appearances.
That's all well and good but they don't follow that guideline with their listings. For example they have included Casey McGehee with the 2B and Gordon Beckham with the 3B. There are some others too that I've come across. Maybe it's just an error they haven't resolved yet, but I found it odd.