I was just waiting for someone to bring this up. Do not be angry with ABC or your local affliate, it is not their fault..
The Indy 500 is not in HD and may not be for a long time as Tony George & The Indy Racing League own the Television Rights.
Tony George set up a production company, Indy Racing Productions and owns Television (& Radio) rights to the Indy 500. IRP hires a local production company to provide camera footage (A pool feed) to a broadcast center where broadcast partners who have paid for the right to air that footage manipulate it and broadcast it to their respective areas.
Pool feeds are very common and used in many live televised events including some sporting events, news conferences, court trials, senate hearings, etc.. Chances are if the event is being televised to more then one area or by multiple outlets it is going to be a Pool feed.
Tony George said in an article about 3 years ago that he will not spend any money converting to HD equipment until it is deemed absolutely necessary.
The bottom line for Tony George is money and broadcast rights for his major players such as ABC do not expire for many years to come so there is no incentive to upgrade. He is going to get the same money from ABC (and other broadcast partners) if he spends millions upgrading to HD or not. When you are a greedy SOB like Tony George who could care less about you and I (we are thieves in his eyes as we watch it on TV for free rather then buying a ticket to his track and putting more money in his pocket).