Football is becoming a more widely used term, referring to the American version, there is American rules, Aussie rules, and Canadian rules football. All of which are similar, though the Aussie rules seems a little more like rugby than any of the others. Of course in Africa, they call it gridiron, to avoid confusing it with soccer.
Though, I play soccer, and the people on my team call it football sometimes. Even our local semi-pro team is called a "football club". So I think it really just depends on who you talk to. Some Americans call it football, some British call it soccer.
Don't the Americans do this a lot? We spell things differently, such as colour versus color. Most Americans also do not use the metric system for reasons I will never understand.