Hop calculations have never been much more than an estimate. Utilization percentages can be manipulated to get closer to actual lab tested levels, but that's about it. In otherwords, it's a ballpark.
Hop isomerization begins to slope off above 60 IBU and with all other things being constant, tops out at about 100. Some factors can increase that by 5% or so, but again, it's a ballpark. Further, most calculations are about kettle levels, not finished, packaged beer levels. Again, manipulating your utilization levels to match where you measure and what numbers you get are important variables for a brewer to consider.
You're 100% correct that your beer doesn't hold that 151 IBUs. But the beer flavor would be changed if you omitted those hops, right? That's a "magic" quality to modern high hop and burst hop rates: the increased flavor and aromatic contributions. The partial isomers are often transformed during fermentation by yeast enzymes.
There is also a major difference in bitterness perception between humulone and cohumulone texture. Cohumulone has a "coarse" or resinous, lasting texture and isomerizes much more easily than Humulone, which has a smoother, short/sharp texture.
The ASBC (American Society of Brewing Chemists) is slowly wrapping its' head around extended heat exposure and increased aroma hopping rates. Thus far, the major research is about the effect of hop tannins, more than alpha acids and aromatic oils.
Brad's decision is a compromise between the major increase in hop extraction efficiency at 95C and the dropoff to <80C where extraction falls quickly towards insignificance. Other than that, there are no reliable models to go by.