Unlike in Florida, the only real "onsite" hotel is the Grand California which has its own entrance to DCA.
Otherwsie, many of the offsite hotelsare actually closer than the other two Disney properties.
We stayed at the Howard Johnson (10 minutes walk) and loved it. As we were at Disney from opening until close 4 of our 5 days I don't think we missed out on any "magic" by not staying at a Disney poroperty.