alot of banks are moving from allowing debit cards to be linked to savings accounts and the other benenfits are obvious when something goes wrong.
A bank usually will not help you much if its a dispute with a debit card, but since with credit cards you have not paid the balance typically they are more likely to intervene in a bad situaution since they have yet to be paid for that purchase..
To answer the question about PINS and dedit cards, the credit cards and Visa check cards are secure if the person taking them is diligent in checking ID and signatures. People actually get mad when they are asked to show their ID --- Duh they are not responsible for BS charges on their cards so they have no incentive to be part of the security of the card. On a debit card there is more chances for them to be screwed over by it coming out of their account and making other checks bounce and so forth.
So the real short answer is that people are strange and will look out for their interests if it benefits them.