Abstruse
Legend
Yes, like I said, the concept of part of the lance going up and hitting a combatant weren't nearly as common as movies and TV like to point out. It was as likely as getting hit by a pitch in baseball and pretty much just as likely to cause serious injury (though less likely to cause death...we do have reports of people getting killed in jousts but I can only think of a couple of times it's happened in baseball, which is played far more often than tournaments were held). I mean it was a sporting event, after all.Ok, welll I see we are going to disagree on this, but it's funny you should mention shattering lances and going through openings in the armor, because I just watched a show about Henry the VIII charging without his visor down, and despite the lance shattering and shards flying into his helmet, it did provide him enough to protection to not be seriously hurt on top of that, despite the visor being up!
And for the record, King Henry II of France was killed in 1559 when his own lance shattered on his opponent's armor (Gabriel Montgomery, captain of the King's Scottish Guard) and rebounded through his visor and into his eye. Same thing happened to William Grey, Lord Wilton at the Battle of Pinkie Cleugh when a pike got through his visor. It didn't kill him but did disfigure him. Nice to have a friend who writes historical fiction professionally

Not all armor was created equally throughout the time period. "Plate armor" can cover a lot of ground, from the clanky suits of armor in the early medieval period to the Roman lorica segmentata to the sort of armor that you pictured above (which was crafted to the man and one of the tests to make sure it was designed well was the ability to perform highly acrobatic calisthenics in it, which is the argument many people use to point out that plate shouldn't have a dex penalty attached).So I disagree, the hits that do get through those cracks are nonetheless less likely to do critical damage. Look at the size of that lance!! It's huge. They made plate armor fitted so tightly, everything was pinned into plate and there was no where to puncture!! I do get your point about the AC threshold being higher in plate so let the crits though, but I disagree.
The "only on magic/special material armor" argument is in response to the scene in the film that started this debate. If you accept that the troll got a critical hit (which I don't agree with and the "action stops and everyone freaks" isn't because of the placement of the hit but because of who it was that got hit with what should've been a mortal blow), then it was the fact it was a mithril shirt that saved him. Something like that adds to the flavor of magic and makes magic/mythic items feel more special than mundane items (which was a complaint in 3.x and a huge point of contention in 4e).This is simple enough to use in real play and has more advantages than not. But the idea that it should be only magical plate that does it...hmmm, they already have that. Nobody goes oooh, and ahhh over some item property that's extremely rare and only provides a small % chance to negate crits.
It doesn't gel well with the KISS philosophy. This is away to get DR on platemail or magic chain/scalemail for "free", in terms of rules complexity.
I'm also not a fan of the idea of too many exceptions as it goes away from KISS. The more "except when" or "unless" or whatever you add to the game, the more complex it gets. "If you roll a 20 on the die, you get a critical hit. Except when your opponent's wearing heavy armor, unless you have a weapon that has the property that says it can get through heavy armor, except when the armor's magic, unless you're wielding a magic weapon..." It gets overwhelming after a while, and if you have to add a bunch of "excepts" and "unlesses" to the game to get that rule, it should be shoved into a module.