The problem itself is seemingly simple and yet so few people are aware of it. I thought I was an educated buyer walking into the world of HDTV, how could I have missed this problem?
The truth of the matter is that this isn't a completely unknown issue.
You can find articles going into greater detail than I possibly could on the net. Here's a few links to get you started;
Basically, the problem is directly related to the television's upscaling and image processing routines. The longer it takes to process the image, the more latency you're going to experience.
Upscaling a 480i image to an HDTV compatible format can take a long time on some televisions.