You're right about the limit, I have mixed them up. It's 1000 USD when arriving by air or sea and 500 USD when arriving by land. Yes, the amount is pretty low.
Regarding visitors, I believe the fees are not really enforced because you can argue that the goods will not stay in the country and enforcement could hamper tourism. But if someone shows up with two brand new laptops still in the box, they'll probably have some explaining to do in case they're selected for customs checks and want to convince them that they're strictly for personal use and it's not an import.
I still stand behind that such rules are the norm, not the exception. The problem in Brazil is not the rule, but the low limits. Regarding EU residents when visiting the US, very similar import rules still apply but the difference is that (1) the limits are higher, and (2) it's easier to take the things out of the packaging and argue those are your personal belongings that you left EU with [1], and (3) the majority are not checked. But even in EU the fact that you're not caught does not mean that the rule does not exist: when you purchase things abroad and they add up to more than your tax-free limit, you are supposed to walk through the "goods to declare" line before leaving the airport, just like in Brazil.
[1] In Brazil if you want to make this argument you have to report your item to customs when leaving the country and then you get a receipt that you can show on your way back to prove that you left the country with it. If you don't have such receipt, customs can argue the item is new and purchased abroad.