Yes, except the 40 kWh customers are essentially getting a rebate ("20 extra kWh" for free). The 60 kWh-ers may reasonably ask why they don't should not deserve

Yes, except the 40 kWh customers are essentially getting a rebate ("20 extra kWh" for free). The 60 kWh-ers may reasonably ask why they don't should not deserve a similar rebate (eg., free upgrade to 80 kWh), especially considering they paid more for the product than the 40 kWh-ers. Note that I'm agreeing that it's nothing to get angry about (and we don't know whether this is something that can be "unlocked"), but I disagree that it's some kind quirky human, irrational response. On the contrary, it's completely rational; it's rational to recognize when something is distributed inequally in a way that favours some people out of sheer luck.