i don't believe that that is the correct way - it may be the most common way, but its not the only way nor the easiest way, or necessarily the best way.
it is just the way pompous people from 100s years ago and victorians etc decided was polite and correct and it has stuck - but we all know how utterly over the top about doing things 'correctly' they were, and how pointless and stuffy it all was - there is a very good reason why that kind of society no longer exists...
knives and forks are not shaped to our hands, to fit exactly into our fingers - they are essentially just sticks with different ends on.
its like saying there is only one way to hold a stick
my sister eats like this, she even sometimes hold the fork like shes stabbing and holds down her meat to cut it... i must admit when i first 'noticed' i was a bit surprised as none of the rest of the family do that ... i guess its just the way that came naturally to her and it stuck ...