Krusty, you should stick to the REX threads cause you've obviously got no idea with regards to the DJ/Skywest gig.
Original plan was for 4 ATR72-500's at this stage. As the 600's came in they were to replace the 500's which were to be shipped off to Skywest. Virgin are making so much dough out of them that they decided to keep the 500's and infact managed to secure 2 extra machines which became available. So at the moment they are in fact 2 extra machines ahead of schedule and by the end of FY12/13 they'll be 6 ahead totalling 10. The 18 you speak of was the original deal and was the end plan, ie 18 machines by the end of the 10 year deal. I now think you'll see quite a few more than that.
As for the finances, I won't even try to explain that, but rest assured its a good deal for both Companies.