I'm not sure I agree - I have always believed Adam was there because of one thing - when Eve ate the apple and nothing happened to her, Adam never questioned what God had said to them (don't eat of the tree - you will die). I have always wondered why Adam never questioned the fact that Eve didn't die when she ate the apple. But ... when he saw that nothing happened to her (Adam had to assume God was lying about it), Adam decided it was safe to eat of the apple too. How would Adam have known Eve had eaten of the apple and didn't die, unless he had seen her doing it. I mean, if she had just simply told him later, would he really have been convinced enough to eat the apple anyway?? . . . I don't think so. This reason alone convinces me Adam watched her eat the apple.
These actions by Adam also convince me God holds the husband responsible - mainly because Adam did not try to stop Eve from eating, and he did not go to God and question why nothing happened to Eve; Adam assumed it was okay for him to also eat - even though God had told him not to. I believe God then said to Eve "what have you done" because Eve never reminded her husband of what God had said, "if you eat you will die"; which I do think was her responsibility.