Many decisions such as diverting will be done in conjunction with dispatch, opps and the flight crew...usually not just the CA's decision. Other things as you mention, holding and such, are the CA's call and they do not get too much hastle about it, unless it is way too cautious. Example would be eveyone and their mother is shooting approaches into an airport with bad weather but one crew wants to hold.

The truth about line flying, as many of you know, is if you can land you will. If you can get through the line of storms, you will.