The "infant cradle" or bassinet on Singapore or any other carrier does NOT replace a car seat as far as safety is concerned. They are not secure and babies should be removed in turbulence.

For the record, I've "cheated" by leaning across and holding the baby in the bassinet but I was required to remove him/her.

While turbulence poses the more common threat, the most dangerous portions of the flight are take-off and landing (with much greater forces). So that's when it's important the child be restrained. If a child is sleeping flat, a seat belt can be placed around them.

Basically air travel is so safe there isn't a huge amount of data to prove or disprove various safety options, especially when it comes to children. That's why you find so much variance from company to company (infant restraint policies, brace positions, etc.)

Ideally, all children would be strapped in for the entire flight, in an infant restraints, but realistically, especially for those of us who fly long-hauls, it's just not practical.