LOL, yeah it's a myth. Hell, I don't sleep through yet, it's just that when I wake up I don't go and harass the other members of my household to help me get back to sleep (except the cat - she's fair game).
There are some babies who sleep through the night but there's no guarantee that it will continue. No baby is 'easy' all the time in every ways. Some sleep well but they're finicky sleepers, some are easy when they're younger and then turn into monsters when they're teenagers, some 'difficult' toddlers breeze through the teenage years.
If your baby won't sleep through it's not because you're doing something wrong and if your baby does sleep through it's not because you did something right - it's jsut the luck of the draw