Well I suppose a phonology that happens to be exactly the same as ours is more plausible than an alien species that looks exactly like us, but still, it gulls me that somewhere along the line, DC just threw up their hands and declared a no-contest on world-building.
And Krypton, Kal-El, and Zod could always be English transcriptions of Kryptonian vowels. Given how hard it is for, say, an American to pronounce Japanese, I doubt Kryptonian is something you can pick up with a correspondence course (though, as noted, world-building fail).