Nascar did pilot that program last year on one of the bigger races, I can't remember which one, last year. I think it was when TNT had the broadcast, but it might have been ESPN at the end of the year, can't remember for sure... I can only assume that it was a success and so they tried it on the Indy 500 this year. It's a great option for sports racing fans!
The IRL has been doing the "Side By Side" as they call it at least 3 seasons now. It is a by product of the open wheel civil war and nobody watching the races. I say this as an open wheel fan who watched both series and am glad to see a single series.
Miner