People in Europe usually have the VAT included in the advertised price, so I can see how people would be getting their hopes up when seeing the american prices.
I live outside Chicago and in some areas around me the sales tax is >10% (10.25 in the city I believe). The fact that you see what your paying in taxes every time you buy something makes it harder for the politicians to raise it too high.
Edit: Fixed Typo
It's good that they do have the charge listed but I still feel like most people are not aware how much of their bill went to the VAT whereas in general around here you can't possibly miss it.
People may not be reminded about it constantly, but they are definitely aware of it.
Additionally, sales taxes vary widely state-to-state, so for an that has the same MSRP everywhere in the US, it seems to make sense not to advertise actual tax amount.