Great post by fourlittlebirds. ITA. I think women start in different places and that the bonding process is much more easily interrupted for some than others.
I have had two vaginal births, but my first was traumatic, painful, medicated and Pitocined. The second was a beautiful homebirth where I was not messed with at all. I always suspected that my difficulty bonding with DD had to do with the birth, but after DS I was DAMN SURE it did. The difference was monumental.
I don't know if this helps at all, but sometimes I think about this and one thing that helps is to look at the bond I have with DD now and know how hard I worked for it. I feel proud of it--it is an accomplishment--whereas with DS it was almost embarrassingly easy.