If any captain did not, or did not have his F/O carry out a walk-round and a subsequent problem came to light, he is on a very sticky wicket indeed.
Sorry, but it is Airmanship.
If anyone neglects it, thinking "Oh, it'll be ok - it got us here, didn't it?" then I hope they'll tell me before I ever fly with them, because I never, ever will.
On turnaround, I've notived a boot ripped to shreds that had happened during the previous sector. Even when the aircraft has just had a check from an engineer, I still walk round. That way, I've noticed oil filler flaps left open by them...
Neglecting a walkround is lazy, is p!ss-poor airmanship, and, as far as I am concerned, is grounds for dismissal, being gross negligence of duty.