In PB, are all carbs created equal?
Does it matter if your 50-100 grams of carbs comes from dark chocolate or from veggies?
Variety is the spice of life.
There's more nutrition in the veggies, there's more pleasure in the chocolate.
What a lot of people on here say is "sugar is sugar is sugar" (I tend to agree with them). The carbs in veggies and the carbs in chocolate are theoretically just fiber, starch, and sugar, all in differing quantities and ratios. In reality, that bag of carrots or that bundle of zucchini will take you a LOT longer to go through than that bar of chocolate, keep you fuller, and is more nutritious. Theoretically, a bar of chocolate is the equivalent of juicing a bag of carrot and then removing any nutrients. In reality, the chocolate just can't hold it's ground against the veggies. Eat the chocolate if you know you won't go overboard, but it pretty much counts as empty carbs and sugar with a few phenols and antioxidants thrown in, kinda like red wine. That's why they're rare indulgences.
For the really simple answer: refined sugar isn't a primal blueprint food, but veggies are.
I think Mark makes it clear that you should choose your foods mostly based on what provides the best amounts of the nutrients you need (in which case I'd choose vitamin- and mineral-rich veggies over chocolate), but another goal of the PB is to make sure you enjoy the food you're eating (which is why the 80/20 rule is in place, to allow some treats). He also calls this a veggie-focused diet, and I'm pretty sure his carb ranges are based on the assumption that you're eating your carbs mostly in the form of fruits and veggies, so a lot of those grams of carbs will be fiber, which your body processes quite differently.
Here's how Mark divides his carbs: http://www.marksdailyapple.com/carb-pyramid/