There are lots and lots of startups that succeeded. They prove that the idea behind them was good just as much as the implementation and marketing and all that stuff were good.
Then sometimes a 'new' startup appears that just copies one of those ideas, puts it in a new market and is just as successful as the former.
For example in Poland we have an internet auctions site that is way more popular here than e-bay, but certainly is based on it. They just were on this market first, so they got the biggest piece of the pie.
Now the question - what's the value of such things? They are very little innovate, on the other hand - coding takes time. The time that's wasted on rediscovering things that others did before, on fixing long-time known bugs.
Seems like a big waste-of-time when I look at it this way.
(I'm not talking about bussiness 'value' of such project, as launching a site on new market is usually a good bussiness).