In Warband when you defeated a noble they usually escaped instantly, ie. you had only a relatively small chance to capture them at all (25-35% I think from memory). Didn't matter if you personally split their skull open on the battlefield and stood over their twitching "corpse", you still usually failed to capture them.
That was annoying then, and high escape rates are annoying now. Would be a bit less annoying to be told they had escaped rather than them just disappearing, which has caused some confusion. It also becomes less annoying when the player understands that putting the prisoner in their dungeon works better than carrying them in your party, so we feel some efficacy about it and can get the escape rate lower through our actions.
Assuming the stated escape rates are checked once per day, I'm expecting it won't be too bad after the latest changes.