Hatespiders I don't believe all those eating (about 20 people) were just painfully shy. I actually think they were ignorant and bloody rude! Also, my dh and I were only quietly asking a little question such as, "Have you known X (the hostess) for long?" or, "Do you live quite near, or have you had a long drive?" Surely someone who isn't morbidly introverted can reply civilly to that without it causing them too much effort?
Unless its a case of crippling social anxiety/shyness (which does exist but is not that common), then being conversational in a social setting is something you should make yourself learn as an adult. I think I was about 19 when it clicked that if I was invited to something, I should make an effort to be a good guest, and that basically meant the easy task of trying to talk to people and make pleasant conversation. Its not a lot to ask...
I've been in similar situations to you three times, and they left me so utterly depressed and feeling unwelcome that they have always stuck in my mind. One was when I tried to introduce myself to my new neighbour, a local farmer, and his wife. I stuck out my hand and said "Hello, I'm Chandler" with a smile on my face. And both of them refused to shake hands with me! I was later told that they had lived in the one place all their lives and have obviously never left home to go out and work with other people and lived a pretty primitive life. Even so, I don't think shaking hands with someone is that difficult!
Another time I was at a New Year's Eve dinner with 3 friends. We were sat at a larger table, and they all turned round to look at us as we sat down. I stuck out my hand and introduced myself to the man next to me, and he turned away and completely ignored me! Not a word! It was incredibly embarrassing. My friends fared much the same, fortunately a couple who had been stuck on the end of the table, and in the end, it was such an unfriendly, awful experience at New Year, that our main topic of conversation was how unfriendly the rest of the people there were! It didn't even seem as if they all knew each other! It was very...odd. One of the oddest nights of my life and one I hope never to repeat.
I've also been ignored as a single woman going along to a dance to meet people - one experience of that is enough for me!