I'm only guessing and don't want to speak for him but I'm guessing he is building it 3x's stronger than needed to support the given weight (so a stand for a 55 is strong enough to hold 150g of water if needed) or something along those lines. Given that a a stand the size of a 55 tank wouldn't hold a tank the size of a 150.
I agree. I overbuild everything. Plus I just enjoy building the stuff and most of the time it actually turns out ok!
Edit: Guess I was right! Posted up while I was typing.