Samsung Galaxy S III (AT&T)
"the first memory card slot supporting up to 64 GB"
I've had a 64Gb SDXC card in my GT-i9100 Galaxy S2 for over 6 months already. Every version of the S2 should support any 64Gb card as well.
No one should expect (unless they enjoy buggy products) a company to officially support something they've never even had a chance to test.
So, yes, no company has advertised it before now. That's correct. Even though it may work on older phones; also correct.
But when it's "not supported" because it's never even been tested, (because it wasn't actually possible to test when the phone was being developed,) then you are taking a real risk that you may lose data due to some unforeseen bug.
You can't blame Samsung for not wanting to be held responsible for losing footage of your kid being born when they didn't even have t...