The widow(er)'s limit (also referenced by the acronym RIB-LIM) is actually the 82.5% rule, not the 81% rule, and it is surviving spouse-gender agnostic. As I understand it, the survivor benefit of a spouse whose deceased spouse claimed SS early is limited to THE GREATER OF the amount that the deceased spouse was drawing or 82.5% of the deceased spouse's FRA benefit.
I noticed this additional amount when I ran my and my DH's numbers through opensocialsecurity.com. We will be drawing similar amounts of social security at FRA. As usual, the recommendation for us to maximize our benefits was that one take SS early at 62, and the other take at 70. But I also ran our numbers through the "Alternative Claiming Strategies," with both claiming at 62. At the bottom of the "Year-by-Year Benefit Amounts" chart, when the chart assumes one of us were to die, the chart shows the surviving spouse would draw his/her own amount but an additional amount labeled "Your Annual Survivor Benefit." It took me a while and a lot of clicking to figure out what this additional amount was, but I think it's the application of the widow(er)'s limit to our survivor benefits.
I could also be totally wrong.