Routes are rated by the FA party. A majority of FA's were on lead. Therefore, the grade listed is for a lead climb.
Using your flawed logic, routes should be downgraded for toprope since you do not have to place gear. Celestial Groove is a 5.9+ on lead, but only a 5.8 on TR. Breakfast of champions is a 5.10a on lead, and a 5.9 on TR.
I've been on 5.8's that have spanked me. Instead of debating the numbers, I try to get my friends to lead them so they too, can get spanked on hard "easy" climbs.