It is very interesting to get an insider point of view.
Wow. Don't they have supervisors? Not at the Gap, I'm sure, I saw the behavior you are talking about there and at the defunkt Tower Records.
I won't even mention Macy's, that has the WORST customer service EVER! Once I was literally given the paper and the ribbon to wrap a present MYSELF. Needless to say, they lost me.
In Europe it really depends about the money. In good stores, where the ppl are union, you get Nordstrom-quality service (at least here on the West Coast, the service there is impeccable, I only complain because they always have sales for men, never for women!) In stores where the assistants are hired illegally, you get the annoyed look, the silent treatment, and the stuff slammed on the counter.