When Will complains about having to mow the lawn, Will's mom tells him he used to do it all the time and had no problem with it back home in Philadelphia. But in the last episode of season 4 "The Philadelphia Story" when they go and visit Will's home in Philly, there was no lawn to mow because he lived in an upstairs apartment. And when they show the outside of the apartment building, there was no lawn in the first place, just a concrete sidewalk.