Software limiting is common. Laser copiers, microwaves, and all sorts of appliances have exactly the same components.
Yep. Ages ago, there was an IBM laser printer (don't remember the model, but I'm pretty sure it was before they were spun off as Lexmark) where it was identical to its faster version but there was either a different motherboard or ROM revision that physically limited the # of pages per minute it could output at max.
I believe in tests where heavy graphics were involved (in which you'd be way below the max ppm output rate anyway), the slower and faster model were identical in perf.
This was in PC Magazines ages ago.
I really do wonder if this press release is an early April Fool's joke...
I can see developing and supporting a 40kWh option costing more than that in R&D.
They already do have one, it's shipped to Toyota for the Rav4 EV.
However, I'd imagine that there's more other work and certification (e.g. crash testing, EPA 5-cycle test for range value, etc.) that would need to be done to ship a Model S with it, along w/the support (e.g. warranty, needing to produce/stock parts for another SKU, etc.) needed.
Also, perhaps Tesla doesn't feel their margins for the car overall are sufficient if they sold a 40 kwh model.