While you're there, pick up a clue about the difference between medial issues and skillset issues, and the different effects having questionmarks in each area have on projections.
Lowrie has always been at least somewhat productive when healthy. The issue with Iglesias is that we aren't sure he's going to be productive even when he is. What that means in theory is that Lowrie has a distinct upside if his health issues are in fact behind him, as they appear to be. I'm not convinced his numbers last year are all that fluky -- certainly north of where he'll be for a full season, but where he'll be for a full season is well above the level, at least offensively, that Iglesias will be able to match as a rookie.
I think the upside on Iglesias is at about the Orlando Cabrera level while Lowrie could potentially reach the level of a John Valentin. It's a question of style choice whether you'd rather have a Cabrera or a Valentin. I'm persuaded that as long as Lowrie's glove is not a liability at short, his bat makes it more likely that he returns high overall value relative to Iglesias, whose defensive skills would make him an excellent substitute while he's learning to hit at the big league level.