bimbo "They are saying it is rude to be invited to the ceremony, basically told to bugger off because they are not important enough for a meal and then invited back to a party. I thought that was abundantly clear ."
this is exactly it. It isn't "evening invites are rude". The rudeness is in the expectation - and yes I've had this, as a summons not an invitation - that you will be there at the church to swell the adoring crowd and then again at the evening do - but dog forbid they feed you in between.
as pp have said, there is a way of phrasing it on the invite that can make it clearer, but certainly the ones I've been invited to that way have involved long explanations of how much I am wanted at the church and the evening do but how problematic it is to feed me because of Great Aunt Mabel and then a list of things I could do for 5 hours inbetween.
as I said, I did it once when I was too young to know better but decided never to do it again. The worst thing was, the meal overran, so we arrived for the reception and were told by venue staff that we had to sit in the lobby. At this point, we realised there were about 6 of us. Of course we don't know who refused the invitation all together, but really, they couldn't find the money to feed 6 of us but they could find the money for what I know the bride spent on her dress?
The couple did email us the following day apologising - we'd waited about 45 minutes in the lobby - and saying "with hindsight we should have handled this differently" so props to them for that.
but as I say, I don't feel the need to attend the wedding of an acquaintance anyway, so now any reception invites are refused. I have had a few people ask why I can't attend though. I invent a wedding I'm already invited to. Save the Date is binned immediately. Unless you're one of my 5 or so closest friends, I don't see why I need to be there.