Difficulty of high school courses varies from high school to high school though. Some AP and honors classes are heavily curved and some are not. Schools have different grading scales and GPA conversions. Standardized tests have to be a part of college admissions in order to better compare students on a "fair playing field".
However, this is where I agree with the study. Key word:
success. The SAT is not the right standardized test for college admissions. If anything, subject tests, the ACT, and IMO AP tests are better predictors of college success. The AP tests are considered to be
college level exams so why not use them in admissions? Ok there are hefty fees as a result of taking numerous APs and many schools offer limited AP courses, but I'm sure the AP system could be overhauled. Also, if AP scores would be used for admission the grading scale would have to be changed to better distinguish students.
Overall though, standardized tests are necessary for college admissions just as they are necessary for grad school. However, maybe the SAT isn't the right test.
Also, I've been thinking about this as I go through the college admissions process myself. How important is the college you attend as an undergraduate? What's the big difference between that top 20 school and your state school? It's really what you do with your undergraduate education and experience. Are you willing to find research/internship opportunities, get involved, seek help from professors, and most importantly study? If so, and if desirable, you can attend a nice graduate school with the hope of securing a successful career in the future.
Maybe we're overemphasizing undergraduate admissions. Will getting that 2200+ really ensure or predict well... anything? Will getting into Harvard complete your life or be a sure shot for success? Probably not. It's really what you do with what you have. If you are that determined and motivated, a standardized test should not hold you back.
Anyways, the SAT isn't a predictor of college success or any success for that matter, but will somebody please do a study on the ACT for once

lol.