Really, they do. It's pretty much a truism that if you the writer could have condensed what you wanted to say down to five pages, you'd have written a short story. So, we'll just take as a given that you are going to lose a lot of detail in the process of converting your baby into its operating instructions. This is doubly true of pitch sheets (more on those later) and pitches, which have the added benefit of performance anxiety, a live audience, and any issues you personally have with public speaking.
So, first, the pitch. A pitch is the verbal version of the pitch sheet, which is your novel on a page, and worse, it begins with the tag line, also known as the one sentence version. Aiee!
There's all sorts of advice out there on how to do this, what to include in the synopsis, proper format, etc. I'm just going to assume that if you want to look for those things you can, and focus on the key internal emotional context. If you can get that, the rest is an extremely aggravating exercise specific to the book. What someone is really asking when they ask you about your book is not all the fiddly details, though those are important too. What they're asking is .Why should I read this book? What's exciting about the story?
Now, you can never really pick out what will excite someone else about your work, because everyone outside your head interacts with your story in strange and mysterious ways. What you can pick out is what turns you on about the story. For example, I'm a world-driven writer. I do all the other things too, plot, character, theme, prose, etc, and as a part of a pitch or synopses I need to talk about those things. But at core, what gets me going is coming up with a cool world and exploring it through story.
It has been my experience that when I start with setting, and let my enthusiasm about the world drive the conversation, editors and other writers become involved in the conversation and interested in what I'm telling them. Contra, when I start with what I think they want to hear, I bomb.
So, with my just finished novel, I might start out with "It's an alternate World War II novel set in a world where industrial scale black magic— sacrifice magic—has become the most important means of combat." Then I'll go on to give my audience some of the back story of the world because that's where a lot of the cool is-like, there is no white magic, at least not at the beginning of the book. After that, I'll address the specific setting and the characters involved: The Black School, a young mage student, his mage girlfriend, the teachers, the enemy—shape changers from another dimension—etc. As I go along, I'll also explain my themes: industrial impact on environment, the ethics of war, the implications of fighting a genuinely, verifiably, evil enemy, when does the end justify the means?
That's all rough and off the top of my head as I sit here, but it's also the product of a lot of practice. I've been answering the What's it about? question for years on more than ten novels and dozens of short stories. Mostly those questions come from friends, family, and fellow writers, but that's all to the good. If you practice with a friendly and genuinely interested audience, you're going to have better results at crunch time.
The things you're excited to tell your sci-fi buddies about your work should be the exact same things you're excited to tell an editor or agent, because agents and editors aren't the job, they're people who are really interested in the same kinds of stories you are. Neither job is one that someone gets into without loving the genre (Note: the same is true no matter the genre). Run with that, talk about what excites you in the field and what you love about your story and others. You may not make the sale, in fact, considering the odds against any particular sale, you probably won't. But you might make a friend and you'll have a hell of lot more fun.
I'll probably go into more specifics on pitch sheets and synopses later. In the meantime, thoughts? Comments? Arguments?