They've generally lead their previous club to relative success though (whatever that realistically looks like for the club in question)
Aside from this seasons cup run, I fail to see what Martinez has actually achieved. I just don't see what he's produced at Wigan beyond what they had when he arrived.
Well, shall we say for a start he has got them to a cup final this season.
Secondly, as the thread in the world football tells you, he operates one of the smallest transfer budgets, one of the smallest wage budgets, yet still has so far managed to keep them in the top tier at a time when the rich have got richer and the poor stay in their place!
He has 3 seasons managerial expertise on his CV in the top flight and is widely regarded as the man who got the Swansea ball rolling to get them to where they are now.