It's not a question about warranty or even availability of replacement parts, it's a question about opening themselves up to extremely long support schedules, something they have never had to do before. If I call an appliance repairman for a 40 year old fridge, he'll likely be able to find the right replacement part... But that model no longer holds true in IoT. Look at cars (at least in the US)... Auto manufacturers have taken on the responsibility that all of their past models could face a recall, even 15+ years after the fact. (NHTSA still opens cases for cars sold in the '90s). The same would have to be said about Internet-connected devices--specifically household appliances.
The problem is that we're talking about operating systems, web hosting software, network stacks, databases, device drivers, etc., that would need to be supported for, easily, 20+ years. Think back to 1994--what software that existed then is supported now??? NONE. So, imagine you buy in 2014 an IoT refrigerator full of the latest & greatest Android 4.4.x and/or Linux 3.13.x FOSS software--what sort of support would you expect for any of that in 2034??? Would you expect Amana, GE, Kitchenaid, Electrolux, Miele, Kenmore, etc., engineers to be fixing Linux 3.13.x kernel security holes in their 20-year old appliances? FOSS or not, as a consumer, I would expect that appliance to continue to work & not get bricked by malware that was deposited remotely...