From memory he did one on a camping light with a "5 volt" USB output which can be used for any consumer devices. He also did one on some coloured Poundland chargers which he ended up blowing up (on purpose).
The point is, dodgy USB adapters exist in the consumer market. I don't recall a single brand-name phone blowing up or having their port destroyed because of it. Many are designed (within reason) to cop what owners throw at them.
So you expect the phone to have an isolated DC/DC converter inside of it to remain floating even when a crappy chinese mains referenced charger is plugged in? Have you seen the size of isolated switching converters for these kind of powers?
Phones are built down to a price AND formfactor. They have to keep the costs down in the mainstream phones to be competitive in the fierce phone market. Also any high power protection devices require extra board space. With the trend of phones pushing to be ever thinner this space is very limited.
Any decently made phone will survive a lot of static zaps to its USB port, It will survive being charged from a USB charger that is not isolated from mains (But the phones owner might not survive that). But it is not reasonable to expect a phone to survive continuous reverse polarity or 24V on the USB port. Yes it is possible to do it, but might not be worth it. It is the users own fault for using a shitty charger, just like it is the users fault if you put diesel in your gasoline car and complain to the manufacturer when it doesn't run.
But the fact that this hack is possible is indeed horrible design that should have never happened. How fucking difficult is it to get about 2 bits worth of information across a wire reliably.