Absolutely right, but are you seriously going to endure the weight of those tarps in your day pack on the off chance that you might need them? In so many items, there is a relationship between weight, cost, and utility. You can choose any two characteristics.
Im talking flat out no tent using those primary. Also a 8x6 tarp Disappears in my pack. I dunno about the ounces and blah blah blah but What I do know for a definitive fact....I cant tell the difference if its in the pack or not, Which is what actually matters no? not the calculations and number crunching down to the ounces of what my pack may weight.