[jmX]

the cost of a kWh for charging the Volt is your average cost per kW

This again? For his application, that is absolutely incorrect. He was clearly trying to take into consideration the cost of charging his Volts vs the cost of running non-EVs, and for that it all gets billed at the latter tiers (probably some 3 and some 4 in his scenario). Assuming his previous load always put him in Tier4 as he said, the answer to his "how much did my bill go up" its going to be VoltKWHUsed * Tier4CostPerKWH. Simple as that. VoltKWHUsed * AvgKWHCost is totally the incorrect answer for what he was solving for.

 

[jmX]

all you are really calculating is how much your power bill went up

Yes, you're catching on now

which is a moot point in the greater scheme of things.

How is that a moot point? To know how a Volt affects your total energy cost, you need to know how much more you pay for electricity and how much less you pay for gasoline. Solving one part of that equation is not a moot point, it's a necessity.