Its streamed live on bbc co uk/f1 but not on iplayer. You were just looking in the wrong place.
The pinnacle of racing is free to watch all over the world. Other forms of racing are limited to select viewers with access to subscription tv. Subscription television broacasters have more money to invest in HD technology, which is why they are sometimes quicker to convert to future technologies. Therefore, live events that are kept free-to-air will often lose out on quality to live events that are shown on subscription basis.