I think it depends horse to horse anyway. There was a clyde/tb with a roached mane and forelock and he looked incredibly cute like that. I think my horse just has an abnormally large head that looks lost without it, which is why I keep it as long as possible too-- to hide some of his head :)
Honestly it can go both ways. My guy is a curly and sheds out his mane and tail, so he gets his mane and forelock roaches as it's pretty much roached already with him shedding... I prefer them both roached, however its always up to the owner.
It depends on the breed. Here in England it tends to be the mediumweight/heavyweight cobs that have the mane hogged and usually the forelock is taken off as well. I don't think I've ever seen one with the forelock left on.