The few that actually do change the world don't usually set out with that goal in mind. Either that or they don't go out proclaiming they'll do it. They just do it.
Contrast that with the startups coming out of incubators boasting about how they're going to change the world with their.....t-shirt recommendation engine app. Or something of the sort.
And who knows? It might actually be a kick-ass product, have phenomenal revenues & truly help people. But it's not going to change the world.
Maybe it's just my issue with the phrase but I think "changing the world" has become one of those trite, overused Web 2.0 expressions that have become as hollow as a dead tree trunk to early adopters & end users. They've simply heard it too many times before and they know not every company is going to change the world.
The other thing that's troublesome is that it's discouraging people from building cool stuff because they think it's not "changing the world." I've already seen questions on Quora from folks who think their ideas (or even existing businesses) are invalid because they don't feel the company's going to become the next Google or Apple; even though, as someone already mentioned, Larry & Sergey were ready to sell at $1 million for the technology. That doesn't sound to me like someone who wanted to change the world from the very outset.
I don't know. Maybe it's just my issue with the phrase but I imagine there are at least a few folks that feel the same way. Apologies for the tangent.