Santa Anita Handicap: What makes it “The Big Cap”?

The Grade 1 Santa Anita Handicap is considered the most important race for older horses in North America during the winter racing season. Why? Is it due to the purse… the southern California setting… the storied history?
No, No and No. How about one word which is in the title… Handicap! Everyone who discounts “weight” as a handicapping angle just fell off of their chairs. There are plenty of them, including 100% of those who make their living on horse racing channels. Without a doubt the majority of horseplayers ignore weight when studying past performances whether it's a claiming, allowance, stakes or “handicap” race.
By definition, a handicap race in horse racing is a race in which horses carry different weights, allocated by the (track) handicapper. A better horse will carry a heavier weight, to give him or her a disadvantage when racing against slower horses. If you didn’t already fall off your chair, you might be feeling your chest tighten. How can this be? Weight isn’t supposed to matter! Or at least that’s what the majority have been led to believe.
In 2011 "The Big Cap”, Game On Dude (14-1) carried 115 lbs. while the 1-2 favorite Twirling Candy was assigned 122. Was weight a factor? Please don’t go there with the “no DQ” debate.
So if 5 to 12 lbs. doesn’t matter on an 1,100 lb. animal, then why are handicap races written? And how is it that a handicap race is the most important race for older horses during the winter season?
As Mike Meyer’s SNL character, Linda Richman, would suggest. Discuss.
Finally, if in handicap races the weight assigned is supposed to be track handicappers “line” or “spread” to entice bettors to wager on lesser horses entered versus the prohibitive favorite, then the weight (125 lb.) assigned to the 3-5 Morning Line favorite Shared Belief should have been 130 lbs. or more based on how his competitions credentials stack up against his. The track handicapper did not do his/her job. Do you agree?