The approx max TOW of the B737 800 being 80T, why bother putting such values as 102.8T in the table (2000m, 5000ft, 3mm)
Your whole post needs some brain scratching and deep consideration. A quick answer to this question is:
slippery runway adjustments are for performance possibilities not structural weight. You find out what is theoretically the maximum possible and make deductions from that. You may then find that you can still go at max structural. Although 102.8T for B737 does seem fanciful as a start point for 2000m Maybe they have 40k engines.
However, not using max structural weight gives more correct runway performance calculations. This was well demonstrated by one fledgling airline I was with. Their performance dept did just this. The RTOW table topped out at the certified max structural of the fleet. Thus the MTOW dry on a 2500m runway & 3000m runway were the same. When you started making various deductions for go/stop calculations, be it technical or contaminated, you found from a 3000m runway you couldn't make destination fuel, but the local more established airline had no bother. Eyes opened when the performance dept realised their blunder. Suddenly from most of our runways we could still make structural TOW. Ah ha!