Any reasonable grid would also be wired such that the power you generate will first go to your neighbors, if they need it, instead of 'round-tripping' to the utility and back. So, the utility is taking a huge cut even though it isn't really a factor in the transaction.

There are of course large-scale infrastructure costs (you get to fail-over to nuclear/coal/gas/wind/other), but it seems like all of those things should be accounted separately instead of all being lumped into two line items on a monthly bill from your local monopoly.