Many flights across the country have been flying at different altitudes due to "the ash cloud". Being on many flights that adjust altitude flying heights due to time restrictions it would be a possibility that Tiger have cut the height even further. (maybe because they are shunted to the end of the que)
Surely singapore airlines would not cut actual plane safety levels.
This country needs competition within the airlines to keep prices down.

Have you ever been on a "turn around" flight to Adelaide because it's past 11' o'clock (PM)