Pretty soon the weight of those things will actually impact fuel efficiency in a meaningful way. Otherwise why not just drive a tractor trailer around?
This is a cheap, weightless feature that is regularly retrofitted. Don't like the concept? Buy the heated seats outright when you spec the car, it'll get coded into your VO and you'll be able to use that feature right up until we run out of petrol.
I don't see the false equivalency however. Heated seats are technically an extra physical item just like many other features of the car. Some people don't need them, nor air conditioners, nor radios.
Some people may just want a frame, engine and body.
It seems the manufacturer, in this case, has simply chosen to ignore the wishes of those consumers. After all, BMW is known to be a luxury car brand and usually won't target value conscious consumers.
Reminds me of Lee Iacocca's funny, paradoxical quote... "People want economy and they will pay any price to get it". Including fooling themselves into thinking heating elements weigh nothing. Marketing departments will run with this and spin anything they can into extra profit; good on them!
If you want, be my guest and buy the option to rent heated seats from BMW :-)