Transformers still draw power if there is no load on them, albeit very low amounts. but transformers are always transforming when plugged in to the wall. It is very small amounts, but seeing as there are a vast amount of them in use on countless devices these days (this helps the manufacturer get around the regulations placed on internal power supplies, as well as saving them money in production, manufacturing, and the bureaucratic "crap".
Follow the money, bottom line is they still draw power even when not connected, and draw much more power when there is a load connected to them.
Transformers do just that, they transform, and they are always active, the difference is when there is a load connected or not.
With no load the draw is minuscule, then changes when there is a load connected to them. If you were to go thru your house and count the transformers/wall warts, that are not in use, the savings would be tiny, if all are connected, then there is more power being consumed. It depends on how they are used, and your use of them.
The "green folks" say to always unplug unused transformers, but in real life that may not be a convenient move. On the other hand, if you have PSU's plugged in that are never used, (or rarely) you may want to consider unplugging them. The savings are small, but if you have many that just hang there and are rarely used, unplug them and save $2-3 a month, maybe. It all depends on the draw and other factors.
http://electronics.howstuffworks.com/everyday-tech/plug-in-transformer.htm
Most all posts here are valid, it is your choice as to how much power you wish to consume. The Apple is a switching supply, that cycles on and off as needed when the battery "asks" for a charge. You can easily tell be feeling if the transformer is warm, if it is, than it is using power.
