The idea that a startup's successful product will be very different from their initial offering is a bit overblown. Yes, there are any number of high profile examples where this has held true (blogger, paypal, flickr), but there are an equal number of successful companies that got big doing exactly what they set out to do (google, amazon).
Twitter and ning are more current examples who seem to have got it right from the start.
Did Ning get it right from the start? Their focus has shifted (rightly) from creating applications to creating groups using the same app.
Ning still has those features, but few people got very far with their "own take on Craigslist" as their original pitch went. It turns out, of course, people want a great successor to Yahoo Groups or EZBoards a lot more.
This is precisely the strategy of my company. It is a bit difficult to do anything exceptionally well when you're so divided, but it's encouraging to see others trying the same approach we are.
Why is it so hard to make stuff people want? I wish somebody would start a company that solved this problem itself; i.e. a startup that generated ideas for startups.
Twitter and ning are more current examples who seem to have got it right from the start.