The only reason people use schedule 80 piping for aquariums is for looks, the grey is easier on the eyes than white and if you use grey PVC cement it blends in. Otherwise it's a bit overkill to have piping rated to what is it 200psi or something for when we'll never have more than a couple psi at best in the pipes.
Have heard of people breaking pipes or bulkheads mind you so I suppose if you're extraordinarily clumsy then the thicker walls might be a worthwhile investment
