Because on the "datasheet" (seeeeduino garden), Digital ports are called D4, D5*, D6*, D7, D9*, D10*.
they look suspicially like the *PMW-able pins!
then a link to that datasheet along with a page reference would be appropriate.
You have your answer but my recommendation about links and page references may help you and others in the future.[/color]
the stars are tiny - but here they are...