Although the trinity of races Adam mentiones is probably the correct way to view it, it's not the way the title has been presented over here. That comes mostly from Mario Andretti's supporters (and I guess from Mario himself) as he's always wanted the overall win at LM to complete the trio. (Of course, he'd add the Daytona 500 to the list, then.)
I'm all for JV doing the ALMS and LM.