There is more to a hurricane than just the mean wind speed. It has to be tropical in origin, be fueled by the latent heat released from deep convection in a background environment where temperatures are horizontally homogeneous. Once the storm moves into the middle latitudes it moves into an area with horizontal temperature gradients, begins to interact with the jet stream which destroys the organised convection around the eye of the storm. The storm becomes asymmetric in appearance, frontal features develop and the wind field expands but the small core of intense winds is no longer evident. The storm is now getting its energy from the equator-to-pole temperature gradient and is therefore declared extra-tropical (i.e. a standard mid-latitude autumnal low with gales).
Unfortunately the media have a habit of overusing the term "hurricane", sometimes applying it anytime a weather station records a peak gust above the 74 mph threshold. This is wrong. Firstly, hurricane force refers to the 10-minute mean wind speed, not the gusts. Secondly, just because a storm has hurricane force winds does not mean it is a hurricane. An analogy is that a car has the weight of an elephant, but you wouldn't call a car an elephant.
