Well, I don't know if you need to outgear them - but they are certainly more challenging at level than other instances are. Going through vanilla was easy, going through BC was only a little harder (learning to handle certain gimmicks), but Northrend has the only instances that routinely resulted in a wipe unless I was really on my toes.

Northrend heroics are still a big challenge to me - even the entry level ones can result in a wipe still as I gear up.