In some ways your right.. 2W not alot of power is it?
However as a Electricain and an energy concious one, every watt adds up.
If you add all the stand by items up around your home, even at a 1W each add this up over 24hrs a day 365 days a year you have a noticable diference on your electricity bill.
Also many "stand by" modes use almost as much power as an appliance switched on

. (particularly DVD's TV's, Stereos)
So, My verdict, Mac Mini Stand by.. Fantastic! But consider using it responsibly.