all nutrients are not created equal.
a body requires more or less of one or more macronutrients depending on thier individual diets.
also nutrient absorbtion is important, for instance spinach, might have calcium, but it is virtually useless to us humans since our bodies absorb very little of it from the plant compared to whats in it. (which is why milk is still considered the better source- even though most quality veggies are low in calories and high in nutrients).
same with peanuts, they might have a decent amoutn of protien, but its only a decent source of the macronutirent as opposed to dairy, meat, poultry or fish which is an optimal source (well depending on what exact thing is within the group). so a person looking to bulk up would pick something along the lines of fish and lean meat/poultry with a whey supplement.
nutrition labels are a rule of thumb, not hard and fast #s. but without our own personal labs, thats the best we have to go by.