Think it's a dog thing mate, some do some dont. Never had one not chase a hare though. Maybe they know hares don't go down burries, maybe they love them more, maybe dogs are smarter than we give them credit for
i had a lurcher x lurcher,and when he reached about 3yrs old, and when i used to try and get him to run rabbits on a fence line he would stand and growl at them,yet he would approach them on the lamp because he knew they would maybe hit the fence and he had a chance of catchin them, but on all bigger quarry,as you said it could be f****n miles away and he would be off like a rocket..