About the Olympics and Davis Cup and so on: in those scenarios it is understood that the athlete is representing their country. You would have to be one of the best in your country to get on the national team, and since that team represents the country it makes sense that the country would feel honored if their athlete does well or dishonored if their athlete does poorly. And when an athlete represents their country it's also understood that the country has helped them out - since the country has put some resources into making the athlete as skilled as they are, congratulating the country is a natural thing to do (although you should still congratulate the athlete of course!).
But for speedcubing, shellie's right on the dot: your country really does not affect your cubing potential or training, and furthermore you do not represent your country. It's not like each country chooses its best cubers to send to a given competition - there's no "Polish team" that trains together, just a bunch of really fast cubers who happen to be from Poland. Poland itself didn't do anything to help them along, and I agree that it's silly to cheer for the country when it put no effort or resources into making Tomasz a better cuber. I think if you do that you are just taking credit away from Tomasz for his amazing accomplishment.
So, congratulations Tomasz!