There are of course numerous factors which can lead to these type of incidents. Some contributing factors are possibly:
- use of non ICAO phraseology (the norm in the USA though).
- Over rapid delivery of clearances by controllers.
- A tendency to clip the first part of the call sign when initiating a transmission.
These busy U.S. airports have to move a lot of traffic. In their endeavour to keep things moving, many controllers resolve to speaking much faster than they in fact really need to. Couple that with the additional traffic information they have to reel off prior to giving what should be a relatively simple take-off or landing clearance and you have a recipe for misunderstandings.