Not KVC, but another great option to avoid manually iterating over a collection is NSArray's and NSSet's makeObjectsPerformSelector: and makeObjectsPerformSelector:withObject:. So, you could:

[classes makeObjectsPerformSelector:@selector(@"autorelease")];

or

[people makeObjectsPerformSelector:@selector(@"setCompany:") withObject:@"Apple, Inc."];

[people makeObjectsPerformSelector:@selector(@"setDepartment:") withObject:dept];

The first example isn't as short as your KVC form, but feels less like it's abusing the frameworks. It's also probably more efficient.