Wake turb. B737-800

[alatriste]

Winglets reduce wingtip vortices and thereby induced drag so that specific range is increased.
If the above statement is true, Why 737-800 is considered a "heavy" for separation porpouses if its weight is well below 136.000 Kg? Winglets should reduce the power of their wingtip vortices and, therefore, the wake turbulence behind it.

Thanks again.