People like to dissect ideas and pitches because that's a lot easier to do than assess the competence of the founders. (Via for example, recommendation letters, but that's a whole new topic).
Try doing this: Read "Founders at Work" or some other collection of startup stories, and try to identify any pattern in the initial ideas that were reasonable predictors of success.
I am sure you will scratch your head for a long time before realizing that it's all about the founders: how they adapted to the circumstances, how they dealt with the tough times, etc. (Ask the very author of the post above!).
My family is full of successful entrepreneurs in totally different market segments (ice cream shops, uninterruptible power supplies, ornamental rocks, etc), and frankly if I didn't know them I'd think they'd all flop: their markets were saturated at the time, they were non-experts, and there was no clear "competitive advantage".
I love the following quote from my cousin (the most recent and already very successful entrepreneur in the family), when talking about how he dealt with all sorts of difficulties with his company:
Sometimes I'm afraid of what I might want in the future. Because it seems like if I really want something, there doesn't seem to exist anything I can't have. (Loosely translated from Portuguese).