I think engineering knowledge is an important factor, going from the time of the first 737 to the A380, there was a huge development in engineering techniques. Better material knowledge, more advanced modeling methods (such as Finite Elements) and better knowledge of structural optimization have improved the situation. Especially with windows, where a lot is happening due to stress concentrations, this improved knowledge makes a difference.
This means that bigger windows might still lead to an increase in weight, but there will be a less severe weight penalty than the same windows using B737 age techniques.