Hi James
If you can get hold of a AOM (you can find a copy on the net for 737-800) the manual goes in some detail as to why aircraft use reverse thrust.
You are right
in that the use of the reverse thrust helps reduce the huge load on the brakes, as you can imagine brakes on a 747/767/757 or A340 are very costly to replace. Greatest load is present at highest rate of knots, so deploying reverse thrust once you have main gear touch.
The level of brake modulation is calculated and the force required to slow aircraft down at a set rate is dependant on whether reverse thrust/spoiler deployment has taken place, so if no reverse thrust or idle reverse thrust is used then the force required by the brakes is that much greater.
Anyone remember what happen with that Qantas flight that overran on a wet runway landing BangKok?? no/idle reverse thrust or autobrake set to 1 or 2 rather than 3 or Max?