Sometimes popular songs are edited by the person in charge of music at a competition to change the tempo and/or pitch and I have run into the same thing many times.
You can get CDs like this on the internet (not many on iTunes unfortunately), that have fixed tempo specifically for competitive dancing.
And it's not realistic that you should expect yourself to be able to dance any song at any tempo. Sure, the more skilled you are the more that will be possible. But the range is there for a reason--so that the character of the dance and figures will be danceable consistently by everyone. Just by adding a couple of measures per minute (or removing), it drastically changes what's possible to do within an appropriate character of the dance (say, dancing slowfox to american tempo, or american VW to int'l tempo, or dancing waltz at 34MPM instead of 30MPM).