It was established in an earlier episode that Frasier's apartment is directly beneath the penthouse. In this episode we see his bedroom is two levels from the top. Either the penthouse has two stories, or someone made a mistake.
Marty and Houghton state that they're going to a double-header baseball game. However, double-headers are almost always played to make up games canceled due to rain. The Seattle Kingdome, as an indoor stadium, never lost games to weather.