Juan1: It would be very, very expensive for manufacturers to provide handmade, expensive top of the line fins and even then you would not be sure that the fins provided would to the taste of a particular customer (who fx may prefer Vector over Deb). Then it would be better just to not include a fin, and I think some manufacturers do this.
But Starboard take a lot of time developing fins and as mentioned use designs from the top guys like Curtis, Deboichet etc. From there mass production manufacturing is tuned and developed all the time to make the fins delivered with the board better and better. As I said in my first post, I think they are VERY good now, a lot has happened since 06. And if you look at test results, iSonics do very well with their original fins.
BUT, when it comes to the last few to % of performance, an original fin from some of the top designers will still be better. Some of that will be "pure performance" and some will be that when you buy an aftermarket fin you can also choose a style that suits your particular sailing style. That is why the pros use these fins.
So, in summary, you can be sure the fin(s) delivered with the board will make it justice. As Geo says, the original fins are also developed to suit the boards but also be very all round, ie fit many sailors not just a particular style. When you're tuned in on the board and confident in your sailing you can maybe try to borrow some aftermarket fins and see what you think yourself.