Normally I'd ask why he hasnt played more than 15 times for Argentina given defence is their weakest point. But then again its Argentina and they consistantly pick squads and teams that are half as good as they should be so thats no slight on him. Must be politics. But I do raise the point again about Madrid earning so much money from his sale... If he's such a good CB that we should be signing him if there are concerns over Vidic, why arent Madrid signing him to be first choice at half the cost of what we'd have to pay? Talk about a bargain right?
He has played in all the WC2014 qualifying games for the past 12 months, 90 minutes every time. He his one of their first-choice CB's at the moment. Given what you and jojojo say about him in Racing Santandar then I'd guess he's either a vastly improved player or Argentina has fewer options now than they had in the previous seasons, which doesn't seem the case as they've been traditionally skint there or a long time.
So while he may have reached the NT late, he is an Argentinian International at the moment. South American teams also tend to allow their European-based players to skip a lot of friendly games due to travelling issues so they end up with less caps than they would otherwise.