Interestingly enough, the term does not even appear in the official 2015 World's Largest Steppers Contest Rules and Judging Criteria - at all! Nope, not one single time. Dancers are not required to perform it, and judges are not required to detect or rate it. Regrettably, "musicality" is not officially required. In fact, even the word "music" appears only twice among the Rules and Judging Criteria.
However, rather than calling it a mistake or oversight, it may more likely be that the producers of the WLSC have discovered something about the audiences that attend the WLSC - musicality does not sell as well as acrobatics, flashy turns, and dramatic flourishes. Given the focus on the "homerun move" and watching and waiting to see it - audiences can even experience a sense of disappointment and being under-whelmed when performers (while executing good dance and musicality skills) fails to deliver that sudden dramatic acrobatic moment. There are Five (5) categories in the official rules and judging criteria. They are: (1) Originality, (2) Synchronization, (3) Footwork, (4) Appearance, and (5) Showmanship.
Judges are instructed that "Originality" should not be confused with creativity and that all movements should be executed "in time" within the basic pattern of the dance. You could almost reach the conclusion that this criterion is suggesting musicality - at least regarding timing - and the cadence of the basic pattern. However, without mentioning that points will be deducted for not dancing "on beat" leaves the door open for some judges and audience observers to conclude that the cadence of the basic pattern of this dance is founded on the "down beat" (3rd and 7th quarter notes in the 8 notes of a musical measure). Judges are not necessarily required to deduct points for dancing "off-beat", but are required to deduct points if you start Ballrooming or Jitterbugging. (Wait...isn't the Jitterbug a forerunner of the Bop, and the Bop is a forerunner of Steppin'? But I digress...)