Weasley jumper vs school jumper

How come when someone uses the term "jumper", it is automatically assumed that they are referring to a Weasley jumper? In the last film, for example, Hermione asks her daughter if she has her jumper: Perhaps she means her school jumper? Even so, Hermione seems to motion that she is referring to the jumper that Rose is wearing, though I could be wrong. AlastorMoody (talk) 08:51, July 17, 2012 (UTC)