because the first thing Rogue does is remove his healing ability. hence, when her power starts to draw on his life force, he cant heal. cos hes lost his healing ability
thats why all his fresh cuts re-opened and the end of the first.
I have, somewhere up in the loft, and in issue of Xmen where the team (as it was at that time..Havok, Physlocke, Wolverine, plus Captain Britian (who was visiting cos his sister had just regained her sight) were taken to another dimension to go on a mission through some citadel for an alien being to fetch a crystal. this citadel could read their hopes and fears and defeated them all, one by one, except wolverine. the bad guy met wolverine by the crystal, and ripped out his heart, killing him. But a drop of wolverines blood landed on the crystal, and provided his healing factor with enough power to rebuild his entire system. he beat the bad guy using the god like powers of the crystal, and refused the temptation to be a good..wishing his metal skeleton and claws back into himslef, he then destroyed the crystal. turned out it was a test of mankind.
the point? well, given enough of a power source, his body can rebuild from a drop of blood.