Yeah. That's about 2GB initially allocated, 4GB maximum. This looks like Java's "out of the box" configuration; my laptop has the same specs.
Still doesn't explain why 8GB are allocated.
We can try using another tool to inspect what's happening while CellProfiler is running. You'll need the process ID (PID) for CellProfiler when it's running. You can use
jmap (should be available with Java) to inspect the heap as CellProfiler runs. Assuming you have a 64-bit Java, the command to run is:
jmap -J-d64 -heap PID
-J-d64 flag if your Java is 32-bit.
Does anything seem off?