I also wonder, if The WB DS pilot had gone to series in 2004, if we might be lamenting its failure to make the cut to The CW just as the fans of such WB series as Everwood are now? Though, of course, that's something we'll never know...
I believe that if had been successful, like Supernatural, it would've been picked up. The CW seemed to want to go with their established shows instead of taking a risk on several new ones like Mercy Reef (I always thought MR was a dumb idea, honestly). Next year I would expect more pilots on the schedule because they have a couple veteran shows that won't be on much longer (Gilmore Girls, Smallville). They'll need new shows.
I've read that a couple of the shows - I think One Tree Hill and Veronica Mars - only received a 13 episode order for next season because of their low ratings...maybe they'll hang on to Mercy Reef as a possible mid-season replacement. I haven't heard that they thought the MR pilot was bad, it just seems like the was no room on the schedule.
With the DS situation, I personally believe that they used the excuse of the pilot being "unsalvagable" because they merely wanted to try a new direction with their network - hence Jack & Bobby and The Mountain. Straight dramas. I believe someone at one point said they were moving away from franchise/cult shows. And of course, a year later, the only new hit they had come up with was Supernatural - gasp! A cult show! I'm not sure they'll be as quick to dismiss the cult/fantasy type shows again. Two of their biggest hits (Buffy & Smallville) and their only recent successful new show (Supernatural) fall under that category.
I'm addicted to Supernatural. Can't wait until it comes back in the fall.