A couple years ago Pheasants Forever held a habitat workshop in Ames and one of the classes was pond managment. It was taught by one of the DNR's pond guru's but I dont remember the fellows name. Anyway, I specifically asked him about the requirement to allow the public to fish if you stock your pond with DNR fish. He said that was one of the biggest misconseptions people have and that it is kind of a gray area. His explaination was that you CAN deny permission to anyone you want. If your buddy from work fished there once 5 years ago thats good enough. I have always heard the same as you but according to him it is not true.
As for the DNR regulating a pond owner on his own property I agree that is a little bogus as long as the fish are not taken off the property. Like Mole said, its not like those fish are going to run over to the neighbors pond tommorow, and therefor are not really public wildlife. A pond really seems no different than a fenced hunting preserve in that respect. Those operations do not have to abide by season dates, weapon types, harvest quotas, heck you dont even need a license to hunt them as far as I know. Not saying you dont need a license to fish someone else's pond, but it doesnt seem right to require a state license if the fish are not kept and transported off the property.
Still, as Bowmaker said, I think common sense would prevail if you encountered a CO while fishing your own property.