Humour is essential to any sitcom but what is funny can vary from place to place, country to country and person to person. In American TV Sitcoms such as Malcolm in the Middle or Will and Grace etc the humour tends to be more obvious with a lot of farce or slapstick and exaggeration. British humour, it can be argued, is a lot more satirical and wordier. American TV Sitcoms tend to be for specific audiences rather than generalised family audiences. Friends is aimed at older teens and twenties and grew up with that audience into their thirties. Malcolm in the Middle is aimed at the younger teen audience. American humour tends to be for a specific audience.
A criticism of both American and British Sitcoms is that they fail to properly represent black people or any other ethnic minority group. There was The Cosby Show in 1984, made in the US, was about a black middle class family rather than a white middle class family. No racial or cultural issues were covered in the series. In Britain Love Thy Neighbour first shown in 1972 seems cringe-makingly racist and crude if watched today. In the 1970s when it was first broadcast it was meant to be a real attempt to represent ethnic minorities.
In Till Death Do Us Part, a biting satire by Johnny Speight first shown in 1965, peoples racist attitudes were challenged. However, Alf Garnett became the darling of the more racist West Ham supporters and some racist chants could be directly traced back to that character.
All About Me, in 2002-2003 was the first TV Sitcom to actually include a variety of different cultures and disabilities. There was an Indian mother and children, a Brummie father and children with one son in a wheelchair.
Ageism is dealt with in One Foot in the Grave, first shown in 1990, but includes a rather stereotypical view of the grumpy old man that developed into an institution with Victor Meldrew. Waiting For God, which also appeared in 1990, was full of witty dialogue and attempted to dispel the view that old people were past it.