The key to liberalism is the belief that if we would just improve services, all the children would be above average.
Keillor's use of this idea has an added meaning that makes it richer, I think, and not an example of the above. It is not only that everyone favors their own children just a bit and sees even the average child as something better. The opposite value is in play as well: don't be too full of yourself, don't put on airs. You're not some genius, you're just above average. When both ideas exist in tension, I don't think it's such a bad thing.
*Title stolen from Thomas Sowell.