I agree. Very unusual for the element to go. Try doing a search for GL1800 heated seats. Among other things there is a fix for the factory seat heaters which invovles soldering a resistor to increase the heat output (Fred Harmon). When they first came out apparently there was a big problem with very low heat output from the factory heaters.
I have aftermarket seat heaters and while simpler in design, 2 heat settings, it puts out big time.
The seat element has been faulty in the past,just because You haven't heard of it doesn't mean other have not had the seat replaced under warranty after the dealer has checked or replaced every other part related to the seat to get the seat working again.
No-Honda does not sell just the element.They only sell it as a whole seat.
Just like you can't buy "A" piece of the rear shock.you have to buy the whole assembly.