Tom and George finding out that there wives are cheating on them in the same day is almost just to judge their character. Nick means that no matter who you are you act the same, only in this case Tom thought it out more then George so that he wouldn't have to get his hands dirty. Tom thinks that daisy is cheating on him because she doesn't love him any more. George thinks his wife is cheating on him because he's boring and doesn't give her what she wants.