Originally Posted by JW10S
Sometimes the federations make deals with manufacturers for their team competitions. It's usually just for the team warm-up suits. An example is Russia and their Bosco Sport deal--Maria Sharapova wore Bosco Sport warm-ups in her Fed Cup matches even though she is a Nike girl. It is very common. The Serbian federation could have made a multi-year deal with ST that is still in effect. The Czech Republic Davis Cup teams wears Alea warm-ups.
I am wondering why Tipsarevic always plays in Fila, though...could be the warm up part...
I am not sure about the other cases...