I've never been to a real dinner party; but then, I'm just now at the age where dinner parties become part of the social repetoire. Americans don't do dinner parties, really; they do the idea of dinner parties. At least, this is what I've heard from people who've attended such things.
Apparently, the Young Adult Dinner Party is the social equivalent of the Bad High School Play, brimming with forced and stilted performances. Everyone is fixated on how they are supposed to act, and what they are supposed to say. Everyone pretends to know something about wine and cheese, and while no one actually knows anything about politics or current events or history, this is discussed enthusiastically; everyone has an articulate ignorant respose to someone else's articulate ignorant statement. Playful banter is discouraged; sexual suggestion is forbidden. Even if you are the designated Foreigner Invited for Purposes of Displaying the Worldly Sophistication of the Hosts, you can only get away with so much bawdy behavior before people start squirming in their seats.
I'm not entirely sure why young adults hold these excrutiating soirees. In part, I suppose, it's to show off their aquiring adult wealth; a new house or condo, pricey wedding china, expensive minimalist furniture. Young adults need to tour each other's homes to get a feel for what keeping up with Jones's is going to entail. They especially want to observe their couple friends in domestic action, so they can either go home to feel smug about their superior relationship, or so that their frustrations are vinidcated and she can go home to belittle his laziness and insensitivity and he can complain about her cooking and her low libido.
And I think that part of the reason these events are so awkward is the curve of the transition. The same people that spent their early twenties drunk on beer and shots, groping strangers, and up until all hours in dirty bars and frat houses are suddenly trying to spend a quiet evening sipping wine with new spouses while holding intellectual discussions. I think the infuriating tension you feel at a young American dinner party is the collective desire of all those in the room to strip down to their underwear, fling the plates off the table, and set up a game of beer pong.