Then we wouldn't need the word "startup" at all. But since people intuitively see a difference between opening up a deli and starting a social network, I think the word has a use.
I think people associcate startups with technology, high risk (compared to a proven business model that has worked a thousand times for other people), and potential for fast growth (with regards to the investment).
I think that's a post appstore or post web definition. I'm all for unsexy startups if they can turn the entire city into a customer and yet not be relevant outside of the city
http://www.paulgraham.com/growth.html