I'm not sure that 24-year old Buffy is going to be as insecure and vulnerable around Angel as 17-year old Buffy was. And while the comparison to 'Smashed' may not be perfect - don't forget, Buffy is feeling a fair amount of self-hate right now. But I don't think the sex here was about self-punishment, but rather clinging to a lifeline.

Though I will say - this is me agreeing with you here! *g* - that she ought to be upset about Angel lying to her, keeping secrets from her, etc. I just think it would be in character for her to bring it up as a snarky remark at some point in the future, when she's had more time to think things through.