[Lmn55d]

In holdem you can be both a small favorite, and a fairly large favorite in a hand. Let's assume that a decent player will be able to identify when he is likely a big favorite and when he is a small favorite. In limit holdem you can only get so much money in the pot at a particular time (usually there's a 4 bet cap on each street). In no limit you can get a lot of money in when you're a large favorite. Thus you can have a bigger edge and thus lower variance, as variance is a function of winrate and standard deviation.

Because of this capped betting, you cannot protect your hand as well as you can in no limit. So even if you are a bigger favorite you will be drawn out on more frequently than in no limit. In no limit you will be drawn out on less frequently, and your opponents will often be less correct when they do draw out on you.

This is my understanding of it at least. Maybe someone can give a better explanation.