[mythtv-users] USB-serial cable for Directv control (stupid question)

[Stephen Sassman]

After reading this for about the 20th time, its starting to make sense
(kind of):

The DirecTV D11/H20 Satellite set top box contains a USB port that can
be used as a serial port to change channels and perform other tasks on
the box. To do this, you need the following cables:

USB->Serial Adapter (usb male to 9 male).
9-pin Null-Modem Adapter (9 female to 9 female)
9 pin serial cable. (9 female to 9 male)

But I still don't understand why I need the last cable (9pin f/m). Can't
I just plug a null-modem adapter cable directly into the serial port on
my PC?