High Pain Tolerance Quality Issue, Typo or is math just hard? Options

[Beetle]

Sorry if it's been touched on before, but two hours of searching and checking errata yielded no helpful results.

from SR4 pg78 (I've got the fifth printing BBB)
"A character who possesses this quality can ignore one box of damage per rating point when calculating wound modifiers (see Wound Modifiers, p.153). So a character with this quality at Rating 2 can take 4 boxes of damage without suffering a wound modifier."

I know I'm an art major, but would someone care to explain how ignoring one box per rating becomes ignore four boxes at rating 2. Should it read two boxes per rating point? Why is it worth 5bp (Rating 1 in other words ) to ignore one/two boxes of damage that naturally would not give you any negative modifiers? Seems to be a steep price to pay for nothing.