Your 100 HP tractor is only 90 HP, but if you got the 100 HP model it would be the same exact weight.
At some point HP goes up to handle the additional weight, but more HP often does not mean more weight. Suggesting more HP gets more weight could seriously mislead some people reading this, especially those who may be new to tractors.
For instance, the TYM 2515 is just under 3000 lbs and 25 HP. The JD 2038r weighs 20% less and has about 50% more HP.