User blog comment:Morganaforever/Reviving your children/@comment-5674726-20121120192514/@comment-5102537-20121120205431

"Uther may also have felt that, if he allowed the use of magic to save Arthur, it wouldn't be a one-time thing and he wouldn't want to repeatedly rely on magic. With Morgana, he could tell himself that it was a once-off and that he'd be able to keep her safe from then on."

Sounds plausible.

However, I think the reason is that the producers probably hadn't planned to make Morgana Uther's daughter at that time and much less having Uther using magic to save her. It probably was done for plot-convenience. Though I have to say that The Crystal Cave is such a brilliant epsiode, in my opinion the best epsiode of the entire show by far.