People make wrong assumptions based on stupidly small and biased samples.  You are a good example of this.  You don't know all stereotypes, in fact it's likely you only know a small fraction of stereotypes and that fraction is biased by geography and self-selection and generally poor education in statistics and/or logic (i.e. not understanding that even if most avid shoe shoppers are women does not imply that most women are avid shoe shoppers).  From this you have generalized that this says something about all stereotypes.  Not only that but I'd wager you probably don't know many of the true values (i.e. How many Americans really are X).