I can see the reason for your confusion. This is always an issue with
security dialogs. In the case of RD, the printer port redirection is on by
default. I guess this is not considered to be a security risk, perhaps
because only printer drivers will be connected to it at the host end.
Anybody ever seen whether a bugbear infected host LAN or PC will spew paper
out of an RD client connected printer? Still--just a waste of paper, not a
security hazard.
So--I think they are only mentioning the connections that they consider to
be possible security hazards in the dialog. I'm not sure why serial ports
are included, but perhaps because some types of security devices are
connected to them?
Your desired mode of operation would be: Check off an item in Local
Resources, and be warned about it in the ensuing dialog. Pretty reasonable,
but not the mindset of the security folks. I had a similar critique of the
SP2 Security Center. I thought that the stuff at the bottom of the security
center dialog should be parallel (in a logical sense) to the three items at
the top. That wasn't how the designers were thinking.
So, for better or worse, the best indication about the port redirection is
from the event logs at the host machine--admittedly not a place many remote
desktop users think to look.