Dan is a wise man with great taste. Baseball in HD is awesome, but soccer and hockey on HDnet (well, they were there a year ago) are un-flipping believable.
I've seen a hockey game on HD Net and it is much better than regular HD because they use the HD screen better. For other channels they use the same camera for the regular feed too and have to fit the action on regular screens. In a pure HD broadcast, they can tailor the shots to fit the HD screen which results in moving the camera less and capturing more action.
For example (hockey):
If the action is in an attacking zone and the feed is broadcast in regular TV too, you have to have the end of the ice in the regular TV field of view, causing part of the HD field to include rows of seats. If it was a pure HD broadcast they could line the end of the ice up with the end of the HD screen and get much more ice in the screen (I think the whole attack zone). So they can just leave the camera still and cover all the action instead of chasing the puck as is goes from blueline to endboards.
In football, in a purely HD broadcast you can line up the line of scrimmage towards one end of the screen and have much more of the defensive backfield in the screen. Now, since they have to use the camera for regular tv, the line of scrimmage is in the middle almost and there is a lot of wasted space on the screen in the offensive backfield.