OP I have been in a similar situation.
I was your wife. I ended up saying exactly the same thing as her because of the grief my DH was getting from his DS and previous DSS (who's wedding it was).
Initially I was invited but then uninvited with the excuse that they were keeping costs down and not inviting partners. This was of course a total lie, DH found out that a friend and his wife (the wife had never met his DSS) were invited. The most likely explanation was that DH's XW had put a stop to it.
After much discussion, DH in torment and talking to the friend, DH decides to tell DSS that he wasn't going to attend alone, we were a couple. DH was relieved. Next phase, DH being ranted at, balled out, called all names under sun by his DS and bride to be.
Witnessing DH's distress I just said go.
I was, and frankly still am, upset that DH didn't just say, when DSS rang with his poor excuse, "oh right thanks but in that case I won't be able to come. "
As some posters have said, you fucked this up with your initial reaction. Your DW is just thinking about you - pity you (and my DH) didn't do same.
I realise this is no help whatsoever.