When you go to place a parts list in a drawing, you have two options - first level components, or only parts... only parts will give quantities for parts right down the sub-levels...
why this isn't available from the Tools>BOM tool in the actual assembly I do not know.
you can export the BOM from off the drawing once you've created it.
means you have to wait for a view of your assembly to generate, unfortunately, but you can get what you want.
cheers,
col.