Yep, Apple laptops keep the RAM powered up until the battery level dips down to 20%, then it writes the contents to disk when the machine sleeps. It's called Safesleep and you can tweak this if you'd like by using a utility called Smartsleep.
Actually, according to the following sources, the content is written to disk _before_ entering sleep. This can be done very quickly because most of the data is already in swap file.
