I'm against providers doing any stretching. Let the user choose. If I want it stretched, add grey panels, partial zoom or full zoom, I can do it with my remote. Forcing me to watch one format that the provider uses is wrong. This is how all three (or four) major networks do it and how all locals do it in my DMA. Several of us have programmed the converters to use bars or stretch during the first few months, and we agreed with what viewers stated: Don't convert. Simply let the user zoom, stretch or whatever. IF it's 4:3 then send it that way with black sides. If it's 16:9, send it that way. If it's 13x2, send it that way with black to fill out to the right ratiop. The blank sides are not sent blank. That is black sides added to the SD to make it 16:9. But, to the user, it is SD and I feel it is best that providers do nothing but add the black sides so the user can do what they want. Then, at full HD content time, we can switch back to normal.
Someday, all of this will be real 16:9 HD and we won't have to worry. Notice on the broadcast networks that more and more commercials during HD prime time are in HD with surround Sound.