I'm from the US but I've spent a deal of time outside the US, primarily in Eastern Europe. In my experience, it is extremely uncommon to strike up conversations with strangers in Eastern European countries.
My wife, having spent a great deal of time in Eastern Europe as well, described it best to me - Americans are extremely good at having a surface-level chat with just about anyone. However, it is neigh impossible for people to get beyond the surface-level friendship. Deep, true, and lasting friendships are hard to come by. Eastern Europeans, conversely are extremely distant and cold at the onset, but with a little persistence, you break through that cold exterior and become almost family.
I could not hide my American-ness abroad and I often was the recipient of stares and mouths agape, but I love chatting with strangers. Everyone has a story to tell and many of those stories are downright fascinating and humanizing.
I would say striking up conversations is possible in EE and US (and everywhere else?) to about the same extent, but just like language, social norms, attitudes, social clues can subtly differ in various places, and a strategy that works in one place may not work in the other, as you say the American style may come across in some societies as a bit aggressive.
source: someone who spent 1/3 of their life in EE and 1/3 in US.
Kinda true even in some western European countries. I have heard the Germans being compared to a cactus. It is tough and thorny on the outside but soft and sweet on the inside.
Cultural normals are one thing, but on a personal level people do tend to enjoy interacting with one another.