Its very much a US thing. Sure other countrys have flags and they like them but Americans really take it to a whole other level. In the uk every school I wen't to had a flag pole but would only fly a flag on special occasions such as sporting events and we would fly sports flags. In America they seem to worship their flag when I see they are scared to let it touch the ground.
From the outside it looks like Americans value the flag more than they value other Americans, in the uk we value brits more than we value the British flag as the flag is just a representation of the people.