The home side took a 16-12 half-time lead with tries from Damien Quinn, Adam Peek and David Tangata-Toa, while Ryan Boyle and James Evans scored for Cas.
With quality kickers such as Sale's Charlie Hodgson, London Irish's Ryan Lamb and Harlequins' Nick Evans around, Bates says even seemingly harmless penalties can become a simple three points for some sides.