yep with DD1 I was in Scotland on my bday!! (i was about 2 weeks by this time, and didn't find out until 6 weeks) I had some big nights in that time. I was worried too until Doc calmed my nerves. I think also that getting pregnant on a big night has merit, it stops the couple "thinking" about getting pregnant, and you're more relaxed, so I can see that it happens that way all the time!
Also I realised with my binges, bubs wouldn't have been attached to me at that time. However I don't think it makes much difference if they are, and it's not like you have a drink and the wholething goes straight to baby!