Actually, Terry, I do not think he should be able to draw blood from the Hulk, either. I just see this whole thing as Logan not haveing enough true physical strength necessary to produce enough force to penetrate the Thing's hide or the Hulks. However, I do recall somewhere in the Marvel mythos that the Hulk's skin, while incredibly resiliant to all forms of injury, actually regenerates more tissue quickly and replaces it more than it is actually impregnable. I could be wrong on that. Undeniably I do not know the Hulk as well as I do the FF. Back in Wolvie's debut in Hulk 181-183, I do not think that any of Wolverine's best efforts were able to draw blood from the Hulk at that time. I'd have to go back and read em again to be sure. I think the whole regeneration thing over invulnerability thing was a cop out to give Wolverine vs Hulk credence in Hulk shedding blood in later battles between the two.
But, I guess its all cannon, now. Regardless how I feel about the subject.