I would have hedges and the like NOT block LOS for Charge purposes.
But that doesn't quite work either. If the enemy starts the scenario behind a hedge and your units don't know they're there, then it doesn't make sense that they're going to go charging the hedgerow. But if those same enemy units were just in sight a moment ago and then backed up behind the hedge, it's not like your dudes are going to think the enemy just disappeared into thin air.
You get the same problems with crest lines - the enemy is there one minute, gone the next, and then your chargers (by the rules) change course and start careening around the battlefield.
Better just to take the rule with a grain of salt, IMO. It's usually pretty clear what a reasonable course of action for the unit would be.