Hmmm - let's see if I can better explain my train of thought
I don't think that the dinner is more worthy of timely attendance - I guess the point I'm trying to make is that the style of party (cocktail) combined with an informal style of invitation feels to me like it might have more of an ebb and flow of guests. More like: Stop by for cocktails to celebrate my birthday - we're starting things at 7:00. To me - that doesn't scream "be there at 7:00" it says "be there sometime after 7:00" - I could easily see some people arriving at 7:00 but leaving at 8:00 and others arriving at 9:30 and staying 'til it shuts down.
Re: dinner - since everyone needs to be at dinner at a certain time in order for everyone to eat together it follows that the "start time" would be stricter. So not a case of a 'higher rating' just a case of logistics.
I really don't think it was deliberately mean or rude. I can understand a group of people saying 'hey let's get together for a quick bite before the cocktail party' and then having things run overtime.
Since the party was slated as 'after dinner' if the 7 or so friends hang out as a group themselves, it seems natural that they would get together and eat first. (I am making the assumption here that the dinner group spends time together apart from the larger birthday crowd regularly - if not, then it's a whole other kettle of fish because the motive does indeed change)
Also: Were the dinner organizers aware that 7 people was in fact 1/3 of the party group? I went to a housewarming cocktail party recently where there were 70 odd guests, had I arrived late with 7 friends - it wouldn't have made any difference at all to the party dynamic since the people I would have arrived with would more than likely be the same people I would be 'mingling' with.
With respect to the formality of the invitation - I get paper invites for baby showers, kids parties, weddings, housewarmings, Christmas cocktails and yes, some adult birthday parties. I just think that the host isn't going to have the same kind of impact calling up friends as s/he would sending an invitation. It doesn't have to be an elaborate invitation - but to me
taking the time to get the details down on paper - or even through e-mail - is less casual than a quick phone call.
Does any of that make sense or am I totally off the deep end?