there's a significant reason for this time buffer.
What time buffer? It doesn't exist in Polish law. The only foreign licences recognised "as-is" are licenses issued by an EU member state. Everyone else needs an IDP (if their country signed the Gevena/Vienna Convention on road traffic - a nice map is here -
en.wikipedia.org/wiki/File:Countries_that_Recognize_International_Driving_Permit.svg
Of course, if you can point me to anything in Polish law which states that short term visitors, holding non-EU licenses from a country which signed one of the conventions can drive without an IDP legally, then I'll eat my words. I don't think you'll be able to though ;)
99.999999% of all people living in America/Canada will never live in Europe for over 6 months at a time.
It doesn't matter if it's "useless" or not - the point is that they have to obtain it in order to be regarded as having a valid licence. Poland may not bother to enforce the law, but other countries can and will. No IDP means they don't have a valid licence in other countries - end of story.
Good luck with the arrogance - it's pretty obvious that you've never rented a car in Europe. The IDP is an integral part of the license if you want to have it recognized abroad - but really, it seems as if you don't even know what an IDP actually is. It's not an "international driving licence" at all.
Anyway, car hire agencies may check, or may not. But if you have an accident in one of their cars, without possessing the required documentation (an IDP) - then good luck!
(gotta love the old "I'm American, the laws don't apply to me")