I stood behind 6 people checking in at the LAX Marriott, they ALL had debit cards and they were all refused. They wanted credit cards only although they would take greenbacks, but not a debit card. Three of them pulled out credit cards and the other three I happened to be traveling with so we just used my card and then they cashed out on check out.
It is becoming more and more the norm to demand a credit card and I am seeing it at check in a lot more.