Yah they support iOS6 on the iPhone 4, but that is the lowest model, so you can expect the lowest performance.
Just like OSX runs on previous iMacs but wont run on iMacs before 2007. Those from 2007 (like my parents) run it, but it's laggy as hell.
It isn't the "lowest model", it was top of the line once. It'd just older, doesn't mean its now the "lowest model"
My 2006 Mac Pro runs Mountain Lion just fine, thank you.