On a local Milwaukee radio station's website, there is a nice laundry list for classic rock fans to peruse. Starting with Summerfest's first year 1968, Steve Palec put together a list of memorable Summerfest moments. (WKLH took that link down, but we all have our favorite moments to reflect upon)
It is funny looking at the list as many of the acts who headlined a stage at Summerfest come back year after year, sometimes moving to a bigger stage, sometimes smaller. Then you have a band like The Steve Miller Band who goes both directions.
If it weren't for classic rock, Bob Babisch and the other Summerfest big shots would have some empty stages, most notably on the Marcus Amphitheater stage.