SRD said:Whenever damage reduction completely negates the damage from an attack, it also negates most special effects that accompany the attack, such as injury type poison, a monk’s stunning, and injury type disease. Damage reduction does not negate touch attacks, energy damage dealt along with an attack, or energy drains. Nor does it affect poisons or diseases delivered by inhalation, ingestion, or contact..
Yes, but it also says it negates *damage* from an attack.
And then clarifies that it does *not negate* a touch attack, energy damage, etc.
Why not just say that it negates physical attacks? because what it negates is damage from physical attacks. Some things that accompany the attacks are ineffectual if damage is not dealt, like injury poisen. Notice that DR does *not* negate the injury poison, it negates the damage, and if all of the damage is negated, then the poison doesn't work