You're right. This is related to how to implement the above expression. I think PREV("A"."net_weight", 0) will make the implementation more unified.
Let's image how we implement PREV("A"."net_weight", 0). This may be separated into two steps:
1) Calculate "A"."net_weight" (suppose the result is result1)
2) Calculate PREV(result1, 0)
This means that the result of "A"."net_weight" is better not be an integer value (this depends on the implementation), otherwise it will be impossible to calculate PREV(result1, 0) as it makes no sense if the first argument of PREV is an integer value.
So for expression A.net_weight > PREV(B.net_weight, 1), the type of A.net_weight may not be an integer value (depends on the implementation) and the compare may make no sense.