Jeff Hamacher suggested that the samurai hairstyle was intentionally bizarre, in order to draw distinction between samurai and non-samurai. This sounds logical.
Many actual historical warrior cultures, as well as modern aggressive subcultures, have opted for "extreme" hairstyles and other points of fashion. The various Germanic tribes in Roman times often indulged in odd hairstyles--note the Suebi tribe and their "Suebian Knot" hairstyle. The Kelts spiked their hair, giving them a very primal look. The 11th century Normans--as warlike a race as there ever was--wore their hair in the characteristic salad-bowl fashion that was so well captured in The Warlord, with Charleton Heston. 12th and 13th century European knightly hair fashions varied considerably--secular knights preferred long hair and were clean-shaven, while the warrior monks of Orders like the Templars and Hospitallers cut their hair short, and grew beards. The Mongols had bangs, but shaved tops. In early 16th century landsknecht armies, the fashion was for short-cropped hair, but extremely long beards. In the 17th century, the Zaporozhian Cossacks had a bizarre haircut called the osoledets, a shaved head with only a toplock, combed forward. 18th and early 19th century European hussar cavalrymen wore their hair with those side braids, as depicted in The Duellists with Harvey Keitel and Keith Carradine. Modern-day biker gangs prefer long hair, while the followers of the British-born skinhead cult insist on either very close-cropped hair, crewcuts, or completely shaved craniums.
David Black Mastro
"The Japanese are the most warlike people in this part of the world. They have artillery and many arquebuses and lances. They use defensive armor for the body, made of iron, which they have owing to the subtlety of the Portuguese, who have displayed that trait to the injury of their own souls." --Gonzalo Ronquillo de Penalosa, commenting on well-equipped wako in the Philippines, 1582.