Reported in bug 3534093 which has been closed with the incorrect comment that the report is not correct. Ezust asked why I think this is true and he pointed to http://stackoverflow.com/questions/4667483/how-is-the-default-java-heap-size-determined
However, as noted in that article running java -XX:+PrintFlagsFinal -version on my 8GB MacBook Pro (Snow Leopard) shows
InitialHeapSize = 0
MaxHeapSize = 132120576 which is in fact 128MB as the max heap size.
java version "1.6.0_51"
Java(TM) SE Runtime Environment (build 1.6.0_51-b11-456-10M4508)
Java HotSpot(TM) 64-Bit Server VM (build 20.51-b01-456, mixed mode)
I think bug 3534093 needs to be reopened.