The WB has a history of crappy moves. First one that springs to mind is canceling Buffy in its prime. Thank God UPN picked it back up. They also really started trying to steal Whedon's thunder on everything, in several major steps. First was announcing that [spoiler]James Marsters would be appearing on Angel, making Spike's death obviously not permanent[/spoiler] before the series finale of Buffy. Second came bossing Whedon into making Season 5 more episodic to attract new viewers, despite having a decent-sized fanbase (which The CW recently did by canceling Reba, its highest-rated sitcom, just for not attracting the audience they wanted). Finally, they canceled it, totally unfairly.
Charmed, on the other hand, I think was ready for a rest. Our three seasons with Prue and our first two with Paige were thoroughly enjoyable, but in my mind, the show went on a downward spiral after Season 5. Just my opinion, though.
Never watched Supernatural, and Smallville never really managed to hold my interest.
I can't state my opinion on the 2004 pilot, as I had no interest and barely any knowledge of the show in 2005.
I think The WB was probably doomed from the start. They were going after the teen audience and when they got great shows like Buffy, when people other than teenagers started watching them, that just didn't fit with their image. They wanted to be the trendy teen network, save their old stand-by 7th Heaven. They were an underachiever network that didn't know what to do with its newfound success, so it simply flushed it down the toilet.