Just had an interesting experience with Air Asia. I arrived this morning from RGN (Yangon) with a connection on Tiger to Singapore. If you fly Air Asia you must clear immigration and customs at BKK, check in and pay 500 Baat departure tax. Apparently it's only Air Asia that does not allow you to merely transit. It's not even the money - it's the!!!!

Welcome to the world of low cost carriers... as I understand it that is the standard model for locos - each flight is a separate thing. There is no connecting, interlining, transiting or anything like that.