If asian and black noses are similar (low bridge, bulbous tip, wide nostrils), why are the results so drastically different?

Asian and African-American noses are completely different, therefore different techniques were used to make the appropriate changes to the nose yet give a natural result.  For many examples and more information, please see the video and the link below

There are many anatomical differences between Asian and Black patients. In particular the thickness of the skin on the tip of the nose is much thicker on Black patients and that cannot be modified with the Rhinoplasty. Other difference is Asian patients have a narrower nasal bone base, and a low radix, so an augmentation on the bridge of the nose has much better results, in Black patients the nasal bone base is wide, the bridge is very low and the results from a dorsal augmentation are less dramatic. Black patients tend to have an important alar flaring and thick nasal ala, that Asian patients usually do not have. Also there are other differences like the shape of the face, acne, etc.

With thick skin noses, whether black or southeast Asian, the skin thickness and technique used determine results.  In general these noses need structure added to the nose, such as rib graft or an implant.