Take EventJoy for example - at a glance, it seems like they're niche. Event registration. You've likely never heard of an event registration company before unless you're in the industry or have hosted an event. It seems like it would be a very small subset of web development available, but then you look at a this[1] and it's obvious that there are literally dozens upon dozens of companies offering very similar services.It seems like there are very few YC companies that are even close to being unique, so I don't understand why they are pushing this as being so important.
[1] http://www.quora.com/What-are-the-best-mobile-event-apps-for-conferences-and-corporate-events