Too much pedantry. If it doesn't benefit the consumer unequivocally, don't fucking do it.
Obviously that's easier said than done for a complex product, but don't expect sympathy when you screw up. Moving away from monolithic all-or-nothing OS updates would certainly help.
So yeah you can choose to keep the old version and loose warranty, cheers!
Im not sure what the legal side of warranty conditions is. But outdated software is potentially a very real cost to the manufacturer in therms of extra warranty work.