The thing is that Samurai, traditionally, didn't wear heavy armor like the category is. It was made of leather, bamboo, reads and cloth. Furthermore, it was engineered to be highly flexible.
This is, of course, talking about the normal samurai (uses swords, doesn't use guns, MAYBE uses bows a little). All three weapons were considered the norm at one point, but swords are the most stereotypical weapon. And swords come with the heavy leather gear.
However, it "is" much, much heavier than a normal leather tunic. And, since games typically have cloth, light/leather and heavy as an option, Samurai usually get put in the last category.
Anyways, you all are horrible, @#%^ed up people
Never underestimate the healing power of a massive dong.