3545 - 3426 = 119 lbs...
119 / 4 = 29.75 lbs extra the tire has to handle. w/o driver.
The only downside of using a lower speed rated tire is handling, I agree most people will never go above 100 MPH anyways. The materials on the tires used for S might be different then a tire used for a T rating. Taking into consideration, tread pattern, rubber compounds used, it might be acceptable if you do a lot of city/ suburb and occasional highway driving.
I say it would be ok as S = 112 MPH vs T = 118 MPH is the next step down so it shouldn't affect things to much since the LX uses a S rated tire, but the EX and higher has more weight to deal with so I guess that is the reason for a higher speed rating? The higher speed rating allowed safer characteristics with the extra weight added?