True. Credit cards offer buyer protections that are unavailable to debit card users. Suppose, I buy a game and the DVD arrives in poor condition, a dispute can be filed with the credit card company and they will stop payment to the vendor until the dispute has been resolved. The debit card offers no such protection, leaving the cardholder to negotiate with the seller to resolve the dispute.
Alternatively, a debit card is more secure in case of physical loss because of the PIN factor(most of the cards require you to enter the pin even after swiping at a merchant outlet), whereas a physical access of a credit card is a thief's windfall moment.
I completely agree with the 1st paragraph - that was my reason for calling CCs more secure for online purchases. Also, it is a simple fact of life that it is easier to dispute a transaction where you are yet to pay (ie CC bill paid to bank) than to get back the money that you already paid (bank account debited on using a Debit Card).
As far as the Debit Card PIN is concerned - it has become a grey area now. Most of the Debit Cards issues by banks like ICICI, HDFC, AXIS etc now allow a transaction to complete without requiring the PIN. If Verified by Visa/MasterCard SecureCode is enabled for the website, they will ask for it. But for sites like Steam, Gamersgate, Paypal etc, which don't support it, the PIN will not be asked for and transaction allowed. So, the security has reduced now, although convenience has increased. That is why I suggested that if someone has to use a Debit Card, then please use one which is linked to a bank account with less money. You REALLY don't want your debit card with 5,00,000 available balance to be misused!