I think most good breeders know what good natural ears look like.
There are a very few that are showing up as 100% american and have a good ear set.
So, they may know what it is supposed to look like, but they aren't producing it!
The thing is, most american breeders are simply going to continue to crop. They wont be scrambling for dogs with a good natural ear set unless the standard was changed to disallow cropped.
I think many breeders are going to continue to crop, but I also think that many newcomers are going to choose not to. (And I do agree that it should remain a choice.) With the change to the standard, IMO, breeders should be looking to produce an earset that will fit either option. (Now, you're right that maybe they won't be - I do tend to get a bit idealistic sometimes!)
So far I have only seen one that was 100% american that won...but I will be the first to admit that there might be a lot of others that I dont know about.
Several, anyway.

There are five 100% North American Boxers who have finished their AKC Championships (in fact, their breeders/handlers were just written up in the January/February Boxer Ring magazine

). Another one won some points a few years ago (before the standard change), though I don't think they pursued a title with him. After the standard change, an uncropped 100% American bitch puppy placed second in her Futurity class at ABC 2005, and there have been a handful of wins (100% North American as well as those with import lines) across the country since then.