Kingfisher Airlines also now has this on their website:

"Please note, currently we only accept Credit Cards issued in India."

FWIW, I had no trouble booking online with my SIN-issued credit card (UOB Visa) for Spicejet and Kingfisher flights during the last week despite the statement above. However, a couple of days later, the card issuing bank (UOB) called me to verify that I had indeed made the charges and mentioned that they were doing this because they had hit by a number of fraudulent charges from domestic Indian airline tickets during the last year. I assume the charges were then verified between UOB and the airlines in question, because no mention of it was made during checkin.