Thanks, I had not though about it this way. While I agree with Frank about the lack of utility of such a marginal effect, it does interest me for other reasons.
So to take this further and leave adjustment out for the moment, Let us assume there is a binary intervention X, a non-confounding binary third variable Z and a binary outcome Y. So with PS weights to balance Z, OR(XY) should also be different from OR(XY) without PS weights so long as Z is prognostic for Y. In other words, if Z was not a confounder we get a marginal estimate that differs from that without PS weights simply because of the differences in distribution of Z in both scenarios. And if Z was a confounder we get the unconfounded marginal estimate and it would also differ from the previous two - right?