The easy nature between saints and Wigan comes from a number of factors-
They've had a period where they've struggled which has passed and now have one trophy in the bag from last year, which has taken the pressure off. They're clearly the best side at the moment.
Combine that with the fact that Saints fans probably have come to terms that we're outside bets for any trophies, so the thought of not winning is less offensive than in previous years.
Also the fact that the majority of posters don't some on hear to wind each other up. Unlike some.