Indeed so - but I think all that probably means is that during previously de-frosting its temp was not allowed to rise to appreciably more that 0°C. The problem with trying to thaw something big (like a turkey) by leaving it in a warm (or even hot) place is that the outer parts will get quite warm (hence a lot of bacterial replication) long before the inner parts have thawed. However, again, that's probably not much of a problem if it is subsequently going to be 'properly cooked'.
Indeed so - anything significantly below about 0°C is probably pretty 'safe'. I think that at temps between 0°C and about -18°C, deterioration of 'quality' (taste and/or texture) may occur, hence the normal temp of 'food freezers'. However, as I said, I've also heard it said that 'quality' will again deteriorate if the temp gets a lot below -18°C - but, as I said, I don't know if that is true.
It's maybe one of those simplified, fits all rules.. They also say, never put any metal in a microwave oven. If you understand the reason for the rule, you can safely ignore it, and more often than not, I do, leaving a spoon, or fork, in a dish.