Explain the irony relating to the Devil's battle with Tom's wife in "The Devil and Tom Walker."

Although Irving writes that no one really knows what happened to Tom's wife, when Tom finds the missing checked cloth with a heart and liver inside and observes the scene near it, he concludes that his wife must have battled the devil and eventually lost--not easily, though, because Tom notices that there were

"many prints of cloven feet deeply stamped about the tree, and several handsful of hair, that looked as if they had been plucked from the coarse black shock of the woodsman. Tom knew his wife's prowess by experience."

The description is ironic on a couple of counts. First, the fact that Tom's wife was so stingy and stubborn that she would have given the devil a harsh time bargaining and fighting fits into Irving's typical, ironic description of the nagging wife.  Secondly, the last sentence refers back to the abuse that Tom often suffered at the hands of his wife, and he almost sympathizes for the devil in regards to the battle between him and Mrs. Walker.